[doberman_52]

Wow, we were just talking about this in psychology a little while ago. Its all in the mind, your morals are what keeps you from doing bad things. If your parents taught you right (morals), you shouldn't kill or steal. But some people do snap and kill etc. It's what you think is right. Every one's morals are slightly different so people do slightly different things. And its also with your need to survive, some people (usually poor) steal to live, to let their family live etc. These are a few reasons I believe.

Edit: I don't think there really is any way to prevent it.