Bible

There's a little bit, loser, so what?

And that's exactly it. Such, let's say, "outcasts" are rejected by people, which subsequently gives rise to thoughts like these:

it's better to just let Armageddon happen

And others (I took the first example I found, I'm too lazy to dig deeper :)).
In other words, "such" people hate the society that rejected them.

Is tearing apart animal flesh fun?
Murder, like any other evil (lesser or greater), is normal if it pursues some goal. Any evil committed for fun is a sign of mental disorder.
So, a maniac doesn't want to prove anything to anyone or get any benefit; he does it because of that very "fun," which is not normal, because such a person cannot think clearly.

I wrote it clumsily – I was in a hurry to take a shower :D
What did I mean? In short, any evil used in the name of good is not bad. And sometimes, evil can only be defeated by even greater evil :)