They have bad experiences with quite a few people of the race and then they just decide to hate the whole race. Anti-Black racists make a deliberate cognitive error. They say that all Blacks suck. They have to say this because when you are that racist, saying that 40% or even 90% of them suck and therefore you hate the whole group seems morally wrong. But if the whole groups sucks then even I would agree that you should hate all of them.
These people still have consciences. It would bother their consciences to hate the whole group if only 40% were bad. In order to clear their conscience, they say the whole group is bad, and now they can hate the group in good conscience.
Seeing racists as evil is an error. Most are not evil. If they were evil, they would not have guilty consciences. They are moral people with consciences like you and me, but they have taken on an immoral view, so they have to justify this to their own guilty consciences, and they jump through some moral hoops to do so.
