I'm a huge believer in evolution (not in the sense that "it happened" - anybody who doesn't believe that is either uninformed or crazy, but in the sense "the processes of evolution are really fundamental, and should probably be at least thought about in pretty much any context").
Unity and self-sacrifice, of themselves, even when fostered by the most noble means, produce a facility for hating. Even when men league themselves mightily together to promote tolerance and peace on earth, they are likely to be violently intolerant toward those not of a like mind.