It’s a pretty cool gambit, really. Load your “cultural distance” arguments with overt discussion of how nonwhite immigrants are undesirable (for a variety of reasons that of course have nothing to do with being nonwhite: either they’re unadaptable in the First World, or they’re adaptable but their migration will rob the Third World of necessary talent). Get accused of racism. Point and say, “See? You can’t raise the issue of cultural distance without being called racist!”