Is religious fanaticism a neccessity in a world where faith literally serves as a shield?

Question

Demons represent the seven deadly sins: gluttony, lust, wrath, pride, sloth, avarice, and envy. They seek to corrupt men's hearts in order to claim their souls to torture in hell. Demons actively tempt mortals similar to how Jesus was tested by the devil for 40 days in the desert. They reveal themselves in different ways: a faint, barely heard whisper, a dream, a vision at the corner of one's eye, and so on. Through these acts, they promise an individual their deepest hearts desire, and push them to indulge in their darker tendencies. They encourage acts such as murder, torture, theft, and other things society deems reprehensible. The more an individual listens to them, the more influence a demon can wield over their actions and thoughts.

At some point, the person becomes so corrupted that the demon can take over their body manually and manifest into the real world. The demonically possessed individual mutates into a monster, and gains a portion of the demons true abilities, possessing increased speed, strength, endurance, telekinesis, and other random powers specific to the demon.They will continue with their acts of violence until he is stopped by force or the demon is banished. The soul of the individual cannot be saved, and is sent to hell to suffer excruciating torment for all eternity.

These facts are well known by society, and have designed counters to prevent it. Faith in Christianity, specifically Catholicism, is the strongest weapon used to prevent corruption. The church encourages strong faith in its people as a way to shield them from being possessed. The stronger a person's faith is in the religion, the more protected they are from corruption. Faith is practiced and increased through regular prayer and worship. Religious iconography and symbols blessed by the church are worn to provide people with limited protection. They are also painted on buildings or other places of worship to ward off evil spirits and their influence. Iconography and symbols are empowered by faith, and only a true believer would benefit from them.This particular religion is the only one known to work, as all other nations with alternative religions have fallen to corruption. All human beings will be tempted by demons at least once in their lives, and Demons tend to prey more on those with weaker will.

With this setup, is religious fanaticism a necessity in order to keep people safe and protected against demons? Is a strict and conservative world view the only way to prevent corruption? How much power would the church weird in the daily lives of people?

Answer 1

Previous question: what power would the Church wield

Make an analogy to the United States today. It has the strongest economy in the world, and it is that way in part because of its ability to protect its people and property through such forces as the military and police (the rule of law being generally recognized by economists as the number one factor for a country's prosperity), allowing its people to enjoy many freedoms and economic opportunities that are unparalleled elsewhere in the world. As a consequence, the US has a high immigration rate since many people are lured by the prospect of upward mobility.

Now, imagine this - because of a strange new worldwide cultural development, the United States becomes the ONLY country that is able to enforce the law and protect itself from invaders. Now, anyone not living in the US is subject to invasion or crime from threats both within and without. These threats could appear from anywhere and without reason, both from inside and outside of your country. Unless you live in the US.

Immigrants would flood our borders and ports, begging to be allowed in. The US would be in a position of complete power over the rest of the world and could ask for nearly anything in order to allow someone in.

Your scenario is even more extreme, as the risk of not practicing Catholicism is not only physical, but spiritual. Everyone and anyone would want to do anything for the Church in order to protect themselves, their children, and more importantly, their souls. The Catholic Church would become the only world authority, and its higher-ups (from priests to the Pope) would be in complete control over the people who use their churches, allowing them dictator-level power.

"Hey, the Church needs 1000 dollars (or gold, whatever your currency is) to continue protecting you from demons this month, can you do that?"

"No, I need to buy food for my kids."

"Hey, no problem. You'll be excommunicated within the week and is that a demon over there whispering to your son?"

Your scenario is more complicated than that, however. Even though your Church is in a position where it COULD do that, whether it WOULD is another story. After all, the demons can influence priests too, right? So you're in a position where the Church has total power over its members, but for any person to use that power would be inviting damnation. This could lead to an interesting dynamic where some priests, bishops, etc. try to abuse their power and others are honestly servants of God out to protect the common man.

Hope this helps.

EDIT: Updated question - is fanaticism a necessity?

Well, yes and no. A much stricter society would certainly develop, as even a small wrongdoing, such as going out for a one-night-stand or fighting your brother, could potentially lead to demonic possession. As such, the Church would start to issue regulations on most aspects of daily life, but unlike last times this happened, the people would willingly and gladly obey them, knowing the consequences of disobedience. However, I wouldn't call this fanaticism, as a religion practiced worldwide where everyone is happy to comply to protect each other's safety more closely resembles something like a national security tax - yes it's a tax and people lose money but everyone is okay with it because of the benefits it provides. Unfortunately, fanaticism could develop where a couple of priests start to become more and more violent in their efforts to control sin. However, these groups of fanatics would die off as a rogue priests who coerces people into compliance through threats or physical violence would be a prime target for demonic possession and subsequent damnation. So the Chruch would need to be careful finding ways to enforce a holy lifestyle without becoming overzealous or cruel.

Answer 2

Power Absolute

I would invite you to take a look at the Warhammer 40k universe as an example of how far the power of a religion that has tangible and quantifiable benefit can extend. Although not everything you find there directly applies to your question, as it is an amalgamation of a thousand different tropes, there are some clear parallels that can be drawn.

Religion as a Shield

One of the major themes of 40k is the struggle of mankind against their darker nature personified by the four Chaos Gods, and the various demons that serve them, that reside in an alternate dimension called The Warp. It is their ultimate goal to corrupt the entirety of humanity, and ultimately consume all of reality itself. They do this though the typical means, promises, lies, and exploiting the weaknesses inherent in the human nature. Once an individual has been seduced into their service, they have pledged their very soul in the service to the darker powers. Those with a stronger will may be willing accomplices, while others are noting more than unknowing puppets being guided by an unseen hand. Regardless, these agents seek to destabilize the veil between reality and The Warp until their demonic patron can materialize, often at a disastrous cost to the mortal.

A typical human stands no chance to resist the power of these demons. Human minds are a weak thing, and it is only though the power of the God Emperor of Mankind, and the strength of the faith in Him does humanity persevere. His power shields the minds of His followers, and acts as a barrier to the power of the Warp. Because of this, the Cult of the Emperor is present everywhere where humanity has spread. It is an ever-present and oppressive constant of human existence. The only alternative to worshiping the Emperor is to become food for the monsters lurking behind the veil. And while most would recoil at the thought, some among the downtrodden masses falter at the promise of something different...

The Result

The Cult of the Emperor, called the Eclesiarchy, thus wields immense power among the daily lives of the people. Their word is law, and to go against them is to be declared heretic, or worse, corrupt. Essentially, they dictate what constitutes worship of the Emperor, and are the ultimate authority on the subject. It is entirely within their power to start a planet wide witch hunt, or to demand that a new cathedral needs to be city sized to appropriately worship the Emperor. Of course, the actual power structure is more complex than this, and depends heavily on the planet in question/who wrote the particular story your are referencing. But this should give you an approximate idea of their power.

Looking at the larger picture of the entire galactic empire of the Imperium of Man, the Esclesiarchy forms one of the main power groups that govern it. Basically, unless they step directly on the toes of one of the other groups, they can do whatever they want. Besides the Emperor, there is no other group that wields more power than them.

Answer 3

Priests as therapists

A society where people bottle up their emotions, squash that jealousy about your sister, smother your burning hate for the way your neighbour lets his dog yap all night...that sounds like a prime material for the deamons to work with and a way in.

So a person's faith would need to be about opening up to someone (probably a priest) regularly - like confession but with a bigger emphasis on talking things out and less on punishment. This would put the church in people's mental health too. People now trust their priests a lot more and they become real leaders of the community but not through fear or squeezing them for cash. The governments, on the other hand, really don't get an option and have to fork out the money (withdrawing the priests from a town would give them evidence enough they need to continue paying the church and listening to their ideas).

There won't be much room for other worship, however, you can't have anyone on the fence about what they believe - you're only as strong as your weakest link.

The church would, essentially, rule whatever country it was in. People would regularly visit their priest and be reporting any strange behaviour their neighbours may be exhibiting. The fear of deamons would be great enough that the priests only need claim a person is on the brink of turning and they could have them killed or at least contained - whether that was true or not.

Answer 4

This is not necessarily untrue as applied to reality

There are lots of people who believe the real world works this way. You may not agree, but given that these people form a significant segment of the human population (about 20%, to one sig fig) it seems a little hard-headed to discount their history out of hand.

Given that the Church seems to report that your scenario corresponds, in a very rough manner, with real life, it seems reasonable to look at what the Church teaches its role in real life is as a guide to what the Church's role would be in this fictional world you are developing.

The Church has a lot to say about the raison d'être of the ecclesial ministry. A summary is given in passage 879 in the linked section of the Catechism:

879 Sacramental ministry in the Church, then, is a service exercised in the name of Christ. It has a personal character and a collegial form. This is evidenced by the bonds between the episcopal college and its head, the successor of St. Peter, and in the relationship between the bishop's pastoral responsibility for his particular church and the common solicitude of the episcopal college for the universal Church.

To elucidate a little, the previous passages state:

876 Intrinsically linked to the sacramental nature of ecclesial ministry is its character as service. Entirely dependent on Christ who gives mission and authority, ministers are truly "slaves of Christ," in the image of him who freely took "the form of a slave" for us. Because the word and grace of which they are ministers are not their own, but are given to them by Christ for the sake of others, they must freely become the slaves of all.

877 Likewise, it belongs to the sacramental nature of ecclesial ministry that it have a collegial character. In fact, from the beginning of his ministry, the Lord Jesus instituted the Twelve as "the seeds of the new Israel and the beginning of the sacred hierarchy." Chosen together, they were also sent out together, and their fraternal unity would be at the service of the fraternal communion of all the faithful: they would reflect and witness to the communion of the divine persons. For this reason every bishop exercises his ministry from within the episcopal college, in communion with the bishop of Rome, the successor of St. Peter and head of the college. So also priests exercise their ministry from within the presbyterium of the diocese, under the direction of their bishop.

878 Finally, it belongs to the sacramental nature of ecclesial ministry that it have a personal character. Although Christ's ministers act in communion with one another, they also always act in a personal way. Each one is called personally: "You, follow me" in order to be a personal witness within the common mission, to bear personal responsibility before him who gives the mission, acting "in his person" and for other persons: "I baptize you in the name of the Father and of the Son and of the Holy Spirit . . ."; "I absolve you . . . ."

And, in non-Catholic language, this is talking about how the priests and other priest-y people exist to operate in a role of service to God and their community, how they are each individually in charge of carrying out God's will and doing priesty stuff and can do that stuff all the time without needing permission or anything, but also how they are a group and need to talk to each other and such, and should take the counsel of the body of which they are a part very seriously, especially the Pope, who's, like, special. So that's how the Church says things are supposed to go, on its end.

On the laity's end, we have:

The participation of lay people in Christ's priestly office

901 "Hence the laity, dedicated as they are to Christ and anointed by the Holy Spirit, are marvelously called and prepared so that even richer fruits of the Spirit maybe produced in them. For all their works, prayers, and apostolic undertakings, family and married life, daily work, relaxation of mind and body, if they are accomplished in the Spirit - indeed even the hardships of life if patiently born - all these become spiritual sacrifices acceptable to God through Jesus Christ. In the celebration of the Eucharist these may most fittingly be offered to the Father along with the body of the Lord. And so, worshipping everywhere by their holy actions, the laity consecrate the world itself to God, everywhere offering worship by the holiness of their lives."

Which, in non-Catholic terms says something like: Everything done by normal people is a part of their relation to God and by extension their role in the Church. It is the role of normal people to live in such a manner as to make holy everything they interact with, especially themselves.

Which makes the point that almost everything involves the Church and Her actions, even if it doesn't obviously involve a priest. So the influence of God and by extension the Church in the hearts of the faithful (i.e. "lands not overrun by demons) is very big, but not so big as to exclude or obviate personal choice and self-expression. What limits the interference of the ecclesial ministry in the lives of the laity, then?

1902 Authority does not derive its moral legitimacy from itself. It must not behave in a despotic manner, but must act for the common good as a "moral force based on freedom and a sense of responsibility":

A human law has the character of law to the extent that it accords with right reason, and thus derives from the eternal law. Insofar as it falls short of right reason it is said to be an unjust law, and thus has not so much the nature of law as of a kind of violence.

1903 Authority is exercised legitimately only when it seeks the common good of the group concerned and if it employs morally licit means to attain it. If rulers were to enact unjust laws or take measures contrary to the moral order, such arrangements would not be binding in conscience. In such a case, "authority breaks down completely and results in shameful abuse."

Now, then, we've looked a bit about what the Church says about itself in real life, now lets look at what's different between your reality and the Church's description of reality.

1. "[demons] encourage acts such as murder, torture, theft, and other things society deems reprehensible." -- the Church teaches that demons seek to drive men to evil, death, and ultimate destruction, and that their influence doesn't have that sort of 1:1 correspondence with 'societally unacceptable'. For example, the Church advocates for theft as a superior moral option in certain extreme circumstances, and thus the idea that demons would encourage persons to commit theft in such circumstances is kinda off from Church teachings. Furthermore, subverting evil social discourse and promoting good social discourse is pretty important in Catholicism. Basically, the Church says Society, even when in communion with the Church != Good and thus counter-social stuff might be irrelevant to the evil of demons, while socially ellipsed issues might, in fact, be really important and targeted by demonic influence. If the world worked more like what you were saying then the demons in corrupted lands would operate kinda strangely, since once murder is normal it no longer is something they can push for.
2. "The soul of the individual cannot be saved, and is sent to hell to suffer excrucitating (sic) torment for all eternity" The Church teaches that God ensures that this only describes persons who die in a state of fundamentally rejecting God. While that might be along the lines of what you are suggesting, the spiritual mutation and such make it sound more like this a possession-type thing, and possession is definitely something the Church says is reversible (c.f. Jesus's exorcisms in the Bible, and the exorcism performed by Tobit as instructed by the angel Raphael, and possibly Paul in Acts 16:18). The immutability here implies that something about your possession process involves voluntary destruction of the will on the part of the possessed, which is a little weird.
3. " Faith in christianity, specifically catholicism, is the strongest weapon used to prevent corruption." -- The Church teaches that faith in God is vastly more important. Presumably that's what you meant, because changing that would make the statement self-contradictory ("Belief in and adherence to A greater than belief in and adherence to B is the best means of salvation. A is (stuff) and greater adherence to B than A").
4. "This particular religion is the only one known to work, as all other nations with alternative religions have fallen to corruption." -- almost but not quite. The Church's position on 'other religions' is pretty complex, but this is close enough I don't think there would really be necessarily any impact at the level of accuracy we're functioning at.
5. "Demons tend to prey more on those with weaker will." -- tradition, in my understanding, holds that it's those with stronger wills and faith and such that are more demonically tempted. The weak-willed don't really need any encouragement to go commit sins, and as long as people are persisting in a state of mortal sin the overall goal of evil is served. This difference is kinda a big deal, because it would mean that the Church's particular relevant ministries would need to be reorganized to serve a very different demographic.

Other than those, though, the stuff should all be applicable, and those don't seem like they'd change terribly much from a non-Catholic perspective, I think.

Answer 5

I think your assumption is incorrect, which actually provides for more interesting narrative paths to explore. Fanatacism is not the mark of strong faith, it is the mark of brittle and weak faith. In effect, I think some demons will be hiding in plain sight as religious fundamentalists, and the question of who has a real shield will be far less obvious... until it's too late!

It has always struck me as odd that religious fundamentalists attempt to stomp out everything which reminds them of temptation. It's a policy akin to having someone grow up in a sterile bubble; of course when they are released into the real world it will be a disaster because their immune system has never been exposed to disease.

Incidentally, people seem to react to sin almost as if it were a disease. Sinful individuals have to be pushed out of the community, it's as if they were contagious. But if true faith immunises one's morals against corruption... then clearly those who seek to remain pure through ignorance and isolation must have less faith even than agnostics!

If someone really has strong faith they can be exposed to temptation, and it will be like water off a duck's back. They will be able to debate and learn about other things, which will help them to alloy their faith with experience and knowledge. The more philosophical and learned the individual, the more likely that their faith will be substantial, as they have sought out and passed many challenges. Where does strong faith come from? Clearly through exercising it. Just like any other skill or talent, one must practice.

How can someone who actively avoids challenge have better faith? That's the mentality of fanaticism; intolerance of exposure to challenge and creation. It beggars belief that one may consider the universe to be God's will, and yet to show absolutely no interest in learning about it; and thus the nature of God. A strictly conservative world view is closer to the deadly sins of pride, sloth, and wrath than you may think.

I'm not sure Catholicism is the right church, or even Christianity necessarily the best religion, to express the characteristics we need for a strong faith. One could venture that Judaism is more scholarly, and thus its philosophical character helps to make it a stronger faith. If any church encourages loyalty to doctrine above individual dedication to faith, then they're far more likely to be corrupted than saved. The overtly zealous church may actually be a hive of corruption!

Answer 6

The answer is it depends on religion.
To answer the questions very fast...

Q: Is religious fanaticism a necessity?
A: No, actually with current values it would only make things worse.

Q: Is a strict and conservative view the only way to prevent corruption?
A: Most likely yes. But not through Faith, but through Cardinal Virtues, Respecting the Ten Commandments, Seven Noahide Laws and other similar spiritual views.

Q: How much power would the Church wield in the daily lives of people?
A: If it goes 'all in' in Faith, and no methods to apply it's Cardinal Virtues, then it would go in pure dictatorship, poverty and slavery. If it applies Cardinal Virtues, most likely a lot of power at the beginning, then it's monetary power will fade away, probably a lot more than in the present time. The credibility would probably stay intact or increase in that case.

First, Catholicism, and as a matter of fact, almost all Christian religions never really used or promoted the Four Cardinal Virtues. Probably because, if they did, there would be less Faith in the Church, and the Church would lose power.
Instead, by overly promoting theological virtues like Faith, Hope and Charity, without cardinality, the Church mostly accomplished the ability to increase it's revenues, instead of actually helping people.
Theological virtues only work, if they are very well backed by Cardinal Virtues.
If theological virtues are not backed by cardinal virtues, it is very similar to how a currency is not backed by gold.
And in regards to the question, if say, any religion would promote, and succeed promoting Prudence, Fortitude, Temperance and Justice, no people would be harmed by some hypothetical 'demons', and as a matter of fact, problems like world hunger, people being poor would be solved in single digit years. And who knows, after that, serious space exploration?
But that would also mean, the end of bread and circuses.
Anyone who would try doing space exploration while keeping bread and circuses would attempt to collapse the Universe, but that's a subject for another story.

The only other religion known that would pursue a form of Cardinal Virtues, is Buddhism. With it's Noble Eightfold path. Of course, there is Tenfold Path too.

Whether you have the Noble Eightfold path or the Cardinal virtues, they are sending essentially the same message. Avoid the Seven Deadly Sins.

Of course, Buddhism was first, 2500 years ago. Cardinal virtues came later through the works of Plato, in it's work, The Republic.
Prudence or Wisdom is called to be the Mother of all Virtues.

So, to answer the question, there is no need for any religious fanaticism that would imply values like 'Faith, Hope and Charity'. Because if it did, it would only keep the Church's coffers more full, thus indulging in greed, and making more ficticious 'demons' happy.
If somehow, 'demons' would appear and drive the world crazy, and Faith would be promoted instead of Prudence, and the Church is here to save you with their faith, then, most likely, the Church is the culprit behind it.

If, however, a religious fanaticism, that would imply the application of Cardinal virtues or the Tenfold path(Because Ten sounds better than eight), or even better, the application of the Ten Commandments or The Seven Laws of Noah(Noahide Laws), then it could not be called 'fanaticism' anymore, but become the new normal.
To call a 'fanatic' someone who would want to be Just, in God's eyes, is blasphemy.

"Love justice, ye that judge the earth"

Source:
en.wikipedia.org/wiki/Paradiso_(Dante)#Sixth_Sphere_.28Jupiter:_The_Just_Rulers.29

Love works with Cardinality. Dante Aligheri with the terms Deficient Love, Excessive Love, and Malicious Love, define the Seven deadly sins.

Allegorically, the Purgatorio represents the penitent Christian life. In describing the climb Dante discusses the nature of sin, examples of vice and virtue, as well as moral issues in politics and in the Church. The poem outlines a theory that all sins arise from love – either perverted love directed towards others' harm, or deficient love, or the disordered or excessive love of good things.
Source:
en.wikipedia.org/wiki/Purgatorio

The core seven sins within Purgatory correspond to a moral scheme of love perverted, subdivided into three groups corresponding to excessive love (Lust, Gluttony, Greed), deficient love (Sloth), and malicious love (Wrath, Envy, Pride).
Source:
en.wikipedia.org/wiki/Divine_Comedy

Faith, Hope and Charity attempt to guide humanity to love. But with no education to not practice deficient, excessive or malicious love, it is all for nothing. This is why Prudence and Justice are the cure for Malicious love, Temperance is the cure for Excessive love, and Fortitude is the cure for Deficient love.

The planet Venus (the Morning and Evening Star) is traditionally associated with the Goddess of Love, and so Dante makes this the planet of the lovers, who were deficient in the virtue of temperance (Canto VIII)
en.wikipedia.org/wiki/Paradiso_(Dante)#Third_Sphere_.28Venus:_The_Lovers.29

Regarding the Church: St. Peter then denounces Pope Boniface VIII in very strong terms, and says that, in his eyes, the Papal See stands empty (Canto XXVII).

Within these circles Dante can discern the human form of Christ. The Divine Comedy ends with Dante trying to understand how the circles fit together, and how the humanity of Christ relates to the divinity of the Son but, as Dante puts it, "that was not a flight for my wings". In a flash of understanding, which he cannot express, Dante does finally see this, and his soul becomes aligned with God's love:

But already my desire and my will were being turned like a wheel, all at one speed, by the Love which moves the sun and the other stars.

Source: en.wikipedia.org/wiki/Paradiso_(Dante)

Through Cardinal Virtues(the equivalent of a compass), Love, Faith, Charity, Hope can be embraced.

Edit: Wiki links are now clickable.

Answer 7

There is a saying that would reflect this "the socialism is on the best way to solve a problem not known in other systems".

First of all, you wouldn't have a problem with faith. You know demons are real, so Pascal's Wager is not existing in this world. There is only infinite gain, OR finite gain with infinite loss. So you can be good knowing that there will be reward. So you are guilty of avarice, lust or greed. Or not if in your world such a thing is not considered by divines as such things.

Anyway, the second problem is - what about ethics? People who draw their morals from philosophy or just the "not being a dick" movement? Their spine may be even better than those of religious people, because they are more pure in their behaviour (as in: not expecting any reward).

Third problem - What if a person strikes a deal with a demon to make good? Find a pot of gold to fund and run an orphanage? Seek knowledge about a poison to help those who have been bitten by a snake or eaten a wrong shrubbery? Will their path lead to doom if they choose it from the start to achieve greater good?

Fourth thing - do you need to believe in an artifact for them to work or are they charged and work no matter who uses them? Is the iconography working on it's own as in don't need faith. Or is it need "charging" and if yes does the user need to have faith for it to work and does he need to have faith in the God or just the item?

To conclude - there would be no Catholicism all together, because people would just need to believe in God and not the wrapper. Also they would not need to hear stories about foul demons, as they could see them and meet them on an everyday basis. The purest source you would have the stronger your force would be.

Also people would die around 200 A.D. as someone would figure that it is better to just use one person who would go to hell to kill thousands of others that would go to heaven.

Answer 8

Not a complete answer, but just an addendum to whatever situation ends up arising.

---

As society eventually reaches the equilibrium[1] where (almost) every living human is either a bodhisattva and therefore free from the worldly desires and temptations that are prerequisites for demonic possession, or a Catholic, you might reach the situation where demonic possessions stop happening altogether. If this happens, people might start to doubt the existence of demons as time goes on, and the necessity of allegiance to the Catholic church would diminish as a result. This would cause those who doubt the existence of demons to lose faith and become more susceptible to possession, thus strengthening the faith of the rest of the community they were part of. Therefore, if humanity doesn't die out, demonic possessions would probably never stop happening altogether.

[1] Assuming the human race doesn't become extinct due to demonic rampages

Answer 9

What are these characters praying to and really why?

If the human characters are constantly harassed by Demons, and therefore they will might be transformed into a monster, they will be hunted down my others of mankind and killed, and THEN sent to actual Hell. The big question here is, why? Why would any of that need to happen just to satisfy the demon, especially when the demon grands you such amazing already when possessed. Is the human still in control at that point I ask?

Here's the real problem with this question: Demon are well accepted in this world, that means instead of religion, they are a fundamental part of science in this world, of course. Why practice any sort "religion" if you just need to be good, what is the Demon saying to you exactly? Once the human realizes this demon trying to possess him/her for the very first time, they go to a priest to get it exorcised. This process is totally free because it would be "greedy" for anyone to charge money for such a life-threatening thing, thus making them susceptible to a demon-possession themselves. And then you realize there is no issue in this world at all. Why believe in a "religion," something requires "faith" when it's clear demons exist, both of those things are needed by some real-world people because they need hope in believing it something bigger and greater than themselves, not when something's obviously, scientifically exists.

Anything that exists in our real-world and is observable by us humans normally is susceptible to science and data research, thus Demons are explained by "Priests" for some reason. If a demon's "monster transformation" can be seen and explained by science, than you have some tough questions yourself.

Really consider this line: "The stronger a person's faith is in the religion, the more protected they are from corruption. Faith is practiced and increased through regular prayer and worship."

This takes place in a magical world where holding onto your good side can simply defeat the demon, so why not just teach the victims specifically how to hold on to their own willpower while being possessed if it works over and over.

If every bad person is a monster (or dead in hell), then the world is completely populated by good people.

Here's a good idea for this story, have a group of characters that uphold the peace who have such "willpower" or "goodness" inside of them, that they entrap the demon that once tried to possess inside their own heart/soul by their own free will. This granted them the demon's powers without being sent to hell, capable of transforming into a "Demon-Monster" due to their own need.

It's like you said, Demons represent the seven deadly sins: gluttony, lust, wrath, pride, sloth, avarice, and envy.

Each Sin has a super-power attributed to itself, free of charge:

Seven Deadly Sins

1. Wrath (red bear) Virtue Patience – Wrath is manifested in the individual who spurns love and opts instead for fury. Users can dismember themselves, piece and piece, and then attach together again by their will.
2. Gluttony (orange pig) Virtue Temperance – Gluttony is an inordinate desire to consume more than that which one requires. Users have telepathic control over rats, toads, snakes, and many other disgusting creatures.
3. Avarice/Greed (yellow frog) Virtue Charity – Avarice is the desire for material wealth or gain, ignoring the realm of the spiritual. Users can be boiled in oil, for they can harness heat from anywhere and store in their body.
4. Envy (green dog) Virtue Kindness – Envy is the desire for others’ traits, status, abilities, or situation. Users have the control over freezing water, the power of pure coldness.
5. Sloth (blue goat) Virtue Diligence – Sloth is the avoidance of physical or spiritual work. Users can wedge themselves into small pits like a snake, they are very flexible.
6. Lust (indigo cow) Virtue Chastity – Lust is an inordinate craving for the pleasures of the body. Users smother their enemies with flames and brimstone, control over fire.
7. Pride (violet horse) Virtue Humility – Pride is the excessive belief in one’s own abilities, that interferes with the individual’s recognition of the grace of the Angels. It has been called the sin from which all others arise. Users can be broken on the wheel however many times they want, for they are invulnerable.

Despond, the 8th Sin (blackness) – Outlook of gloom and despair, chronic hopelessness, the question “What difference does it make?”

Answer 10

In this context, Catholicism offers the greatest protection. This implies that other religions do also, it is just less effective.

Fanaticism could form around overthrowing other, "weaker" religions, in part for self-preservation. "Allowing" people to practice other religions increases the risk of a demon rising and therefore the risk of that evil spreading.

What is unclear is that if this can be actioned in a way that doesn't make the fanatic a target for possession themselves.

Answer 11

That depends on what you mean by religious fanaticism. 1.If you mean that the people care deeply about there beliefs and incorporate it into daily lives and are deeply offened by those who try to belittle it, then the answer is yes.

2. If you mean that people are vilotent toward those of other beliefs or other wise try to put pesure on others to conform to there views then No.

Some things to think about. If only Christian are protected from demons and everyone is tempted at least once, then by the laws of natural selection everyone still alive and human must be Christian. Sense all forms of Christian provide protection from demons there is no need for conflicts for trying to protect are faith because it protects us from demons, because anyone whose views might threaten my protection against demons would probably be taken over demons.

Answer 12

Several issues with the setup:

The stronger a person's faith is in the religion, the more protected they are from corruption. ...Iconography and symbols are empowered by faith, and only a true believer would benefit from them.

Religious faith is unsubstantiated belief in powerful supernatural entities. When demons actually exist and specific rituals are proven to work, there's no place for faith anymore. There's still a place for faith (or lack thereof) in one's own holiness / standing in good grace (and, consequently, the ability to invoke holy powers). However, Original Sin is a prominent doctrine of the Catholic Church; being a good modern Catholic means questioning your own spiritual strength. It's not very Catholic if the best Catholics are people who never go to confession or do penance.

The soul of the individual cannot be saved, and is sent to hell to suffer excruciating torment for all eternity.

Souls are beyond the scope of human experience (aka "don't exist"), and Catholicism states that contacting the spirits of the dead is impossible for humans, so any prospect of eternal torture would have as much effect in converting people as right now.

all other nations with alternative religions have fallen to corruption.

Catholicism is worldwide, it's even in the name. It's not a nation. Catholics live everywhere and Catholic missionaries go almost everywhere, and once demons are popping up, the doctrine is going to (maybe, see below) catch on. Also, in traditionally Catholic countries, many people are "cultural Catholics", not literal believers. China with its ~10M Catholics probably has more aggregate belief than Poland with its ~33M.

The answers:

With this setup, is religious fanaticism a necessity in order to keep people safe and protected against demons?

Fanaticism has to be redefined, of course. The necessity of belief for containing the demonic threat will depend on the severity of the threat and the efficiency of other containment methods. Do psych drugs or therapy work well to suppress the urges that cause possession? What about weed or LSD?

Is a strict and conservative world view the only way to prevent corruption?

Definitely not. Real-life Catholic doctrine changes, have changed and will change, it varies form place to place, from priest to priest, and it will stay internally contradictory at all times. The abstract deadly sins can be argued (the Catholic Left certainly does so) to suffuse conservatism. It can be argued that, for example, universal basic income reduces Greed and Envy; masturbating to porn is less Lustful than secretly imagining your friend's girlfriend naked; and living off capital instead of working is basically inviting Sloth to turn one's body into a sack of semi-sentient lard.

How much power would the church weird in the daily lives of people?

Anything is possible. The church as an organization could gain power, it can be co-opted by governments and lose power, it can completely dissolve in the face of factual knowledge. Considering that Wrath is only one sin out of seven, demons and demonic hosts which don't go on rampages can collaborate to suppress both the church and believers. You decide what works best for your story.