It's very difficult to grow up in the U.S. and not acquire some racist preload. The culture is steeped in racist attitudes and assumptions, the media we consume is full of subtle and not so subtle racist conventions and tropes. It seems to make sense to accept this reality and lose some of the defensiveness. Most people are not at fault for being on the receiving end of this programming, but being defensive, denying the reality, taking general observations as personal insults certainly won't help in personal enlightenment and growth. If somebody directly calls you a racist and you have an emotional reaction, that's pretty good evidence that you need to do some introspection.