On the whole a very good post. But here --

The reason I bring this up is that intelligent people sometimes do things more stupid than stupid people are capable of. (For example, quite recently, several respected geneticists declared that there was no such thing as race - an idea that not even the dimmest kid I knew back in Detroit would have fallen for.)

-- you misunderstand the position that you're criticizing. The claim of the geneticists is not that race does not exist, but rather that it doesn't map to the joints at which geneticists, qua geneticists, find it particularly useful to carve reality. But when trying to understand the social world, within which your kid in Detroit is steeped, Race is certainly a useful way to carve reality. And this is all that people mean when they say that Race is a social concept, not a genetic one.