The "racism is natural" argument?

It is natural in the sense that we are tribal animals, so stick with our own tribe. However this is no excuse. It is a natural instinct for me to punch my co-worker when he is being extremely obnoxious... I wouldn't, its wrong, and my cognitive process overrides my instinct. The same should apply to racism. The world is becoming much more tolerant through increased exposure to other races, and long may it continue.