Why did Hitler want to kill all Jews if he was part Jewish himself?
There is some evidence that Hitler had a Jewish background, but I’ve never seen any confirmation. The more interesting question embedded in your query is why ANY person would come to hate himself and, therefore, express such hate by acting out against his/her real or imagined heritage. I wish I had an answer to this, but I don’t. Let me encourage you to pursue this deeper question for I fear that it’s linked to events like Columbine High School. If you become smart enough to understand the dark side of human intellect and emotions, you may be able to help other souls save themselves.