I dunno Doc, I suspect it stems from overreaction to fear of the unknown.   Somebody is too dumb or lazy to figure out what's going on, and lashes out at any handy target.   That thesis would suggest it's pretty normal and maybe even genetic, even if not constructive.   WHAT to hate may be learned; constructive alternatives probably have to be learned.

But I'd distinguish legitimate anger, which is of course a social judgment.   Some fucker robs or hurts my family, then I'm entitled to anger, if for no other reason than the community consensus that's illegal.   Though getting even works better for me, than just getting mad.

While religious differences may mask territorial or other conflicts, the religious conflict per se is usually pretty damned stupid, in that it doesn't address the real problem.  

But what the hell, if the real problem is overpopulation, then the religious conflicts do just fine at killing people off.