Racism is a part of everyone and is not a disease. It had a very constructive purpose in the day when a stranger would wander in from the jungle who might carry a disease that could wipe out a tribe. I don't imagine it had to happen very often to get the message across that strangers bring bad things with them, so just kill them before they get too close. Now I'm sure there are those that would prefer to believe that it is merely a learned behaviour but there have been too many studies that have demonstrated how many learned behaviours mysteriously manage to become instinctual behaviours over generations. We have seen it in animals why should it be any different for us.
That doesn't excuse it. It just means it's not something we shouldn't have to feel guilty and dirty about if we discover remanents of it in us. It's just something we need to confront and overcome, which we can, because we're supposed to be intelligent.