[kbenson]

For the same reason that people still do things knowing they result in jail time, people will still do things knowing they are wrong. There's probably a few root causes for actions like that (rage, hopelessness, greed, etc), with different levels of how much each one plays in the decision.

In the end, society only functions because the vast majority of people think they are better off following the norms set by that society. When they no longer think this because of emotional tunnel vision or a real lack of hope, whether it be real or imagined, or pervasive or lasting just long enough, their actions are no longer predictable as a rational member of society. Unfortunately, that means in some cases, it doesn't matter what the consequences are, there will still be the occasional incident.