This is what I'm saying though, it doesn't work. You cant discourage a play style you need to encourage another play style. Players who wish to run around killing anyone and everyone should not be punished, its their choice and what makes the game diverse. Having the ability to do and act like someone you would never be in real life, namely a bad guy, is far more appealing in a virtual world than being a good guy. Thats just fact because, as you say, most people are not sociopaths. So what needs to happen is something needs to make the "good guy" style of playing more appealing and encouraged over the other. That's the only way it will work.
Fallout3 did this pretty well. I great example was in the very beginning of the game, you choose whether or not to blow up MegaTon. Should you choose to save the city you get a room where you can rest, store items, receive water very early on in the game. Should you choose to blow it up, you have to wait sometime before you get your player house. The good guy play style is rewarded, but the bad guy play style is not punished. Its just a little easier so it encourages you to save the city.
Edit: Apparently Rocket might feel the same as me, I did not know this
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