> So, what's the argument here exactly?
Many Americans take US-specific cultural concepts about topics such as race, and try to apply them globally, without realising that those concepts fall apart when you try to apply them outside of the specific historical/cultural context in which they evolved. And even in their country of origin, their existence is sustained (in part) by ignoring the existence of people who don't fit into them – so long as those people remain a small enough minority, they can be ignored. If they start to get too numerous and loud, political pressure will result in changes to the scheme to try to accomodate them, through the addition of yet further categories – but failing to address the fundamental problem that trying to reduce the immense biological and cultural diversity of humanity to a small number of coarse categories is a fool's errand.
> I am able to tell the difference between a person from Sub-Saharan Africa, for example, and North Africa.
If you look at the transition zone between the two – places like southern Egypt and northern Sudan – you will find many people whose physical appearance is somewhere in-between the two. You seem to be ignoring the existence of those people.
> China and Europe and India.
Europeans and northern Indians are historically related peoples – they both speak Indo-European languages, Hindi and English are distant relatives of each other. They are both cultural/linguistic descendants of the ancient Aryans, and also have some common biological/genetic ancestry. So what makes them "different races"? Some Pakistanis look rather European – seen most strongly in groups such as the Kalash and Nurstanis – are they a "different race" from Europeans? Why?
The majority of Indians are by ancestry a mixture of Aryan and Dravidian, with greater Aryan ancestry in the north and greater Dravidian ancestry in the south. Does that mean Indians are actually two different races? But the reality is the majority of Indians have ancestry from both–few Indians are purely descended from one or the other–so the idea of classifying Indian people into separate Aryan and Dravidian "races" doesn't work. And don't forget North East India – the majority of people from there have more linguistically and genetically in common with the peoples of China and Tibet and Southeast Asia than with people in the rest of India. What race are they?
> I do get the underlying idea, though. I just think it's naive.
I think your ideas on this topic are naïve.