I have a magic system in which emotional extremes turns people into monsters. What are the possible effects that this magic system would have on a Renaissance-style world?
For example, obsessions can turn a person into a "monster." Sadness, anger, and any other emotion with a selfish origin would be "negative" and turn you into a monster. It becomes easier to become a monster; the closer to death you are. It works best on older or sick people. The younger you are, the less risk you're at. Basically, monsters attack people and possess lower-level intelligence while retaining basic knowledge that they did in life.
Conversely, altruistic emotions turn you into a monster that hunts monsters. However, the altruistic monsters are smarter and live out the vices of who they were before.
Monsters are five times stronger than a human that is very physically fit. Example: a soldier. They also have a durable skin with defensive capabilities comparable to chainmail. They weigh about a ton and would be about the size of a gorilla. Monsters would come in all kinds of shapes.
There are knights/warriors/mercenaries trained to become emotionally neutral, which actually grants them supernatural strength: about three fifths the strength of a monster.
The usage of firearms for defense is increasing, and the need for these trained super soldiers is decreasing.
What kinds of moral philosophy/religion might develop or exist in this context?
Sorry for not making it clear but the older I you get the easier it is to become a monster. So basically, children get a mostly free pass.