That isn't much of an answer. Why do the Muslims hate the Jews and vice versa? Why did the Protestants hate the Catholics? Why do Christians look down on Hindus, Krishna's, and Buddhists? It probably goes back the other way too. I would say there are very few religions that are true to the words of their respective saviors...and that is sad. Please don't tell me that "your religion" is innocent, because none of them are. Right now, there are radical Islamists vowing to kill all of us because we're not with them.
If there is a God, and I truly hope there is, He/She/It needs to start showing-up for work, because this world is a hot mess.