It's so terrible to see, what people are capable of doing, when they are fanatic enough. It seems to be some perverted, but widespread human behavior. Especially when it's about religion. Not only that fanatic muslims (I'm not talking about "normal" muslims here!!!) fight against the whole christianity (and other muslim groups, that aren't orthodox enough for their taste), it's also catholics against protestants (I'll never understand that!). And don't forget the christians in the times of the crusades.
But also outside of religion there's this strange behavior. I'm not that much of a football (soccer-) fan, so it's inconceivable to me, how adult people fight each other, because they have different favourite soccer teams.
So, we're the crown of creation!! Hard to believe that any animal would be capable of being that way.