To be quite frank, my chief objection was that expressions like "such-and-such is a disease" have been cover for prejudices in the past - for example, regarding homosexuality. But more to the point, race is seen as an intrinsic property of the person which cannot be eliminated even if the actual markers of race are eliminated (witness the one-sixteenth rules) - which would make it a genetic disorder which can only be managed, not eliminated. A "blackness" which is treatable is so different from the modern, Western sociological phenomenon we call "race" that it doesn't make sense to talk about it.

So it's a poor example that makes people uncomfortable, in sum.