Racism is ingrained in all of us. Even when its not completely obvious in a particular interaction between people, it is still there, below the surface. There is a natural, or at least initial, distrust when encountering someone of a different race or culture, and this may be a normal defense mechanism. Since there has been such a long history of race hatred and misunderstanding, it adds to the distrust. But once we establish that the other person is not a threat, most people don't have a problem after that. I think thats the difference right there, between a normal persons reaction and that of a racist.