Unfortunately I think you have it backwards. Some people just really, really like to fight, and to purge heretics from the group of pure believers. It also doesn't help that the smallest misstep is sufficient to switch one from "pure believer" to "heretic" in the blink of an eye.

I'll go ahead and link the famous "whale cancer" article from SSC: http://slatestarcodex.com/2014/06/14/living-by-the-sword/