What if he grants the scientific evidence and claims that blacks and whites should be treated differently simply because they are black and white? Suppose he says that blacks are repulsive or that educating blacks and whites together is repulsive to him. Can we say anything other that pointing out that he has failed to point to an objective difference to serve as a basis for differential treatment?

There is one argument that has been used by R. M. Hare in discussing Nazism. We can ask the racist if he would agree that he should be discriminated against if it were discovered that his great-grandfather was black. (This is like asking a Nazi whether he should be killed if it were discovered that his parents were Jewish.) At this point the racist may begin to backtrack. He may say that he does not have the traits of other blacks. If he does that, he must be able to say what those traits are, and we may be able to show empirically that his claims are false.

On the other hand, he may agree that if his grandfather was black, then he, the grandson, should be discriminated against. If he does that, we may have reached the end of rational discussion.