My theory is that white supremacists are so inept and inferior, and so ignorant and unintelligent, they blame their own failures on any scapegoat besides themselves, and are so delusional as to think that if everyone else who was not like them were not around they would be superior at all times.

I think it stems from inadequacy in the bedroom. They can't get it up for their wives and if they do they need to think about other naked men in order to get off. This repressed homosexuality ultimately leads to deep seated anxiety and fear that ethnic men are superior in bed with the white mans women so they take that frustration out on others.