A government develops technology that can be used to remotely control people's brains for mind control. The government decides that instead of enforcing its laws by having penalties for people who break its laws and police to arrest law breakers that it will use mind control to make it impossible for people to break its laws. What would be the effects of such a method of preventing crime?
Total collapse of civilization when mind-controlled zombies are unable to make any meaningful decisions?
Most legal systems recognize that laws must be applied with human judgement. Say there is a speed limit of 55 mph. Clear-cut, right? Build a compulsion into the mind of each driver to never exceed it. Except that one day a motorist transports a pregnant woman and and suddenly the need to get to the hospital becomes urgent. The motorist is no ambulance driver, not even a medical professional to make a diagnosis. He simply decides that there are more important things than the speed limit in that situation.
Now that doesn't happen every day. How about a more simple situation? In the office where I work, we have a cookie jar. The people from the other offices on the floor are welcome to eat a few, within reason. Technically, taking cookies without permission would be theft. We've given permission to take "a few". How does the remote control evaluate the situation?
If the government was benevolent, you might have a false utopia; if it were malevolent, you'd have a One World Order. Standard TV Tropes disclaimer applies: I'm not responsible for any loss of time, consciousness, etc that may arise from using these links.
In all seriousness, a perfect system of mind control means there'd be no prisons, no jails, and no conflict-- so, essentially, no story. Of course, the easiest way out of this is that there are Rebels, people somehow resistant or immune to the effects of these devices, or perhaps the devices have to be constantly powered to have an effect and something disrupts this power supply in a local area...
If you have an imperfect control, you might end up with a story like Logan's Run, where most people accept their fate, but a few actively avoid being brainwashed/controlled/manipulated/enslaved/etc. Perhaps there's something in some DNA that prevents some people from being enslaved, and they happen to be appearing with increasing frequency because of natural selection, resistance, etc. For this reason, "enforcers" must keep a patrol to identify and neutralize threats to this Utopian society...
Of course, you're left with two real choices for a story: either the control is suggestive, where most people submit to it, or the control is dominating, but some natural mutation has rendered a precious few immune to the effects. A completely wimpy system doesn't make for much of a story, nor does any device that is absolutely 100% perfect.
In such a world where a device is balanced, I would imagine that no "laws" exist on the books at all. No prisons exist, and everyone is led to believe that life is, for lack of a better term, "perfect." However, those that are somehow outside the influence know better, and they're probably trying to bring down the system. In return, the system is trying to kill the resistance outright, since prisons do not exist in a supposedly perfect society. Preferably with a weapon that produces only unidentifiable dust on a successful kill (e.g. Logan's Run).
Even though it's been done before, I still find the idea intriguing, so you could tweak the ideas a bit. Again: not perfect technology, some sort of resistance exists, death is guaranteed if discovered, and there's some sort of weakness to the system. Perhaps a covert means of communications, secure, yet vulnerable network points, or even doctors that discover the gene responsible for being susceptible...
I feel there are two key variants of the scenario, one where the state has the power to control the actions of the populace, and another where the state controls their thoughts.
In this scenario, imagine that your motor cortex/neurons are overridden, or your limbs instantly paralysed or whatever, at the moment you begin to execute a criminal action. I'd say this type of control would cause considerably more suffering; the frustration from being able to form intentions but never carry through would be torturous. I'm considering both good and bad intentions here — it would be impossible to veer out of your lane to avoid hitting an animal, and also impossible to punch someone you're enraged at.
In this scenario, I feel people would come to hate the system, but would obviously be unable to do anything outside of the law to express this. Worst case scenario, it might even be illegal and thus impossible to express these negative feelings. "Best" case scenario is a mind-controlling liberal democracy where people are free to write critically about the system, gather peacefully to protest against it, even vote for it to be moderated or eliminated — but the people would be doing all these things at the absolute mercy of the state.
True mind control
This scenario is maybe philosophically more interesting, but potentially difficult to write an interesting story about. Let's imagine that instead of intervening to prevent specific criminal actions, the state is able to control people's mental states, impulses and desires. People may not even be aware these thoughts are not their own, and go through their days feeling a warm sense of community spirit, the sheer strength of their belief in their society combining with the total contentment of having everything they could ever desire to make a person who would never even think to break the law.
To add some conflict, you could do what some other answers have suggested and make certain people immune — imagine the crushing weight of being the only Bart Simpson in a society that is 99.99% Ned Flanders.
While Cort Ammon has a point with his "something that powerful — whatever you want" there are some obvious implications.
Having mind control technology would imply mind-machine interfaces level of technology. Your tech would essentially be an artificial conscience implant. This implies a capability to extend, expand and enhance human mental processes. It would also imply that the technology is mature, safe and affordable. So you can assume full blown transhumanism future with people having instant access to online references, simulations, computation power, communications, and telemetry. They would also have near total control of their own mental processes as limited by anti-abuse laws and safety regulations. And as per premise that control could to some degree be overridden by either firmware or more realistically "the proper authorities".
People with this level of computing and understanding of mental processes would probably be able to off-load that control to mature and safe low level AI processes. So while all kinds of abuse are potentially more intrusive and expansive there is no direct causative link, they might be very liberal with strong privacy or the dystopian exact opposite. Realistically something that can be argued to be either. It would simply be so different that any match to our current social concepts would have to be ambiguous.
Being able to prevent crime implies they have the ability to recognize when someone is about to commit a crime and intervene before any action has been taken. This IMHO implies that they have understanding of the mental processes leading to committing crimes. The effects would be similar to the effect the germ theory of disease, vaccinations, antibiotics, and sanitation have had on disease.
You could assume a huge drop in direct and indirect effects of crime. Indirect cost of crime are fairly large so this would probably show up as on increase in the standard of living and even as a decrease of mortality in certain demographics. By analogy to disease you can assume that crimes would be resistant to prevention and that over time social evolution would lead to increase in resistant crime. You might even have occasional epidemics, that would also be considered as such, where resistant crimes spread from person to person.
I'd like to end by "remember the first paragraph". The society with this technology would be different enough for any real predictions to be impractical. There would be lots of consequences and implications we can't really see since they depend on factors beyond our sight.
Although it might be beneficial to crime prevention,
"...with great power comes great responsibility..."
In other words, this power could be far too easily abused. If someone with not-so-good intentions got their hands on it, there would not be much that could be done to prevent this person from "mind-jacking" everyone into thinking he is the Supreme Ruler of the Universe.
The only real way to avoid this catastrophe is to impose some severe limitations on it. Perhaps, every machine can control only
x people, and there are
y machines in existence, of which the blueprints are hidden somewhere secure. Then,
xy people could be controlled in a relatively secure manner. (There is still a problem of stealing the machines, or worse, the blueprints)