I think some of it is a form of feeling victimized.
They blame their circumstances on the 'other'.
Some are born into a family of racists, and carry that behavior as a badge.
I have difficulty understanding this deep hatred of people for reasons NONE of us have control of, what color we are, what our sexuality is, etc. It's all the luck of the sperm.
That said, these people are driven & a real danger.
They blend in, which makes them more dangerous.
They are our Taliban.