One of humanity's greatest weaknesses is cognitive dissonance. People can convince themselves of just about anything. And in some ways intelligence is a burden here. A fool will just do something with a reason of 'f you, that's why.' It's only the clever man that will even bother rationalizing the villain into the hero, and we're great at it. An interesting thought experiment is to ask people if they'd be willing to push a button that would randomly kill a person somewhere in the world for a million dollars. They'd have no direct accountability themselves and their action would be unknown to anybody else.

People will rationalize themselves into declaring this moral even though it is obviously one of the most overtly amoral actions possible. One friend I have, a rather intelligent guy otherwise, was even trying to create a utilitarian argument that he'd donate some percent of his 'earnings' to life saving charities meaning he'd be saving more life on the net. The fact that if everybody thought and behaved the same way, the entirety of humanity would cease to exist, was a consideration he didn't have a response for. Let alone the fact that he just rationalized his way into justifying near to any deed imaginable, so long as you got paid enough for it.