"There is only one cause of hatred, period: fear."

Strive for simplicity, but learn to mis-trust it.
                           Alfred North Whitehead

I'm afraid, Little Hawk, that your short, pithy answer doesn't quite do justice to the complexity of the human condition: some of the hatred I have seen certainly seems to arise out of a wealth of other causes, some of which 'may' have some form of fear involved. It is just too simplistic to reduce ethnic centrisim, religious intolerance, righteous anger, perceived discrimination and a host of other emotions to 'fear'.