What about the school of thought tat says that it is 'power' that corrupts, and some men (I stresss that it usually men) want 'power' over other men.
It does not take much to turn some men to hatred based only ignorance, there MUST be more to this than meets the yet.
Most people are good and go about thir live's doing things for the right reasons and if you believe in any God, you have to believe that he (your own personal God) helps you to survive life and enhance other's lives whilst we are here. Evil is not just the temptations that we all encounter, some evil is bred.