You're essentially saying you're not going to date a guy because you think he should be dating a black girl. That's ridiculous. Everyone chooses who they want to date.

Furthermore, the whole notion that he should be dating a black girl is a racist notion. It has more to do with a concept of "preserving the black race" or "preserving blackness" or whatever you want to call it, that really should have no place in modern society, any more than an Aryan Nation concept about preserving the "purity of the master race" should.

I would actually find it easier to sympathize with you if you had said, "There are cultural differences between blacks and whites in America that remain and I don't think I have a lot in common with him". That would have been taking the interracial component and explaining why in a purely personal sense it gives you misgivings about allocating your time and energy to a relationship with the person. However, if your personalities are close enough, that should be enough.