Why are people so bigoted?

I asked a question about Obama's IQ and I got lots of responses that quoted phony information (no, his IQ isn't 124, and his SAT's and LSAT's have not been released). OK, par for the course. But what we really struck me is that several posters claimed that he had benefitted from Affirmative Action because he graduated magna cu-m laude from Harvard Law School. Now the truth is, Affirmative Action (well, not AA, it doesn't even apply in these cases, but let's say racial preferences) can help get someone in to Harvard Law, but it can't help them graduate or earn them honors. So -- why are some people so quick to ume that someone who is black benefitted from preferences even in cirstances when he didn't? And is it racist to pretend that someone can become a professor of constitutional law with an IQ of 124 or 115, or do people simply not understand the requirements of that job?