They think that facial features are equally as superficial as skin colour, so it wouldn't matter much. Arguing about skeletal differences doesn't matter either, because you tend to be dealing with people that think the sexes are equal in physical capabilities despite the obvious. If they are retarded or crazy enough to deny something so plainly self-evident, then there's not really much you can do. But if they accept those differences, the main issue is educating them on how genetics can affect character & inclinations, and how, even though every populace has it's own bell-curve/ range of abilities, different populaces do not necessarily share the same range- and it can be mainly caused by genetic inheritance, not something that 'saviours' can fix, no matter how much they sacrifice.