Basically it's another spin on the white-trash/n-word formula, which has been playing in this country for a long time.
WS: In his argument, he is varying geographical location of people's origins to explain differences in those people's cultural achievements. He is doing so, inter alia, to debunk the claim that variation in "race" explains those differences by holding the location variable constant for different "races" and noting that between-race variability almost disappears. That looks like a good argument too me.
Of course I do not feel offended if that )or any other) argument makes some segments of the US population look bad. I have a generally unfavorable opinion about the United States as whole and I do not feel any particular need to stand up for any of its parts, especially those that seem antithetical to anything I value.
Wojtek