Bigotry is a choice. We are not born racist, but many people are conditioned to be so from birth.
Actually, we ARE born racist. A trait which favors people more similar to you is self propagating. Please note that I'm not justifying racism - just pointing out that it's an evolutionary hangover, like many other aspects of our behavior. You might want to take a look at this: implicit.harvard.edu and maybe read this: http://www.newscientist.com/article/dn18761-stranger-danger-at-heart-of-racial-bias.html