Why do people hate other people?
People hate other people because the person they hate is either not very nice to them, or they have a bad history. People should get over their hatred and stop being mad at everyone all the time. People should just get along, because life is short. Why waste time being angry, upset, or hostile to other people. Enjoy your life while you can because you only get one of them.
Hatred is intrinsic to the human animal. It's in our nature to become extreme, and to try to curtail it is to suppress it . We live in a world now, where buzzwords and mantras and breath prayers and cliches and Drew Pinsky and gender studies courses, are being installed like fail safes in people from their first day of kindergarten, e.g. the "bad touch" rundown. In short, postmodernists show us everything wrong with the world, then tell us to be mature in our responses to it...but, ultimately, people are people, it doesn't matter from whence they sprang or what positions they hold. The Primal is the Real; whether it's a behavior for polite company, or righteous in any way, whether "good" people should hate, begs the question, really. All creatures respond "emotionally", on some base level, including and especially Man. If you scratch the surface on the thin facade of fun in others, some of the most mature, polite human beings boomerang into maniacs (the old Tom Green Show on MTV, proved that mind-numbing immaturity alone, can bring out the beast in almost all). And, beyond initial, knee jerk anger, there are lies, grudges and bitterness and a deep well of hate. Where did it come from? The answer varies, but it's too easy to say, "from within the hating individual". Another modern fallacy states that others "do not make us" do anything, but the behaviorism of Skinner easily disproves this, and even est bottoms out with each of us as machines, responding to sensory data. Thus, one hates because he wasn't loved and another hates because she was abused, and another hates because the world is frightening and another, because someone was rude. Hate, the dark of the jungle (or sin, for the faith-based), is stardeep within us, a part--an unwelcome part, granted--of The Human Condition. As far as social interactions, i.e. how we "should" act with respect to the differences we encounter, is not relevant to the question. The question is, "Why do people hate other people?" The answer is, "Because there are other people...and, They are, by definition, not Us."