The "coloured people" thing may show my age, but in as much as I can remember why I used it, was because I think of UKIP type people using it, and I was trying to descirbe their view.
As for it being "inappropriate" I flatly refuse to play that stupid game. I'm not going to hop around changing my language because some the PC brigade want to ban words, rather than do anything useful.
Fact is that as soon as any term becomes common, they leap in and call it "inappropriate".
I do not mean it offensively, would use it to someone's face and have referred to my friends that way. Actually I tend not to think in terms of people's race much anyway, but I suspect that's because I care about the grey stuff in their head, not the brown stuff in their skin.
I take it that the analysis you quote of this term is sarcastic ? It's not even biologically accurate.
White people are more "pure" than "coloured" people. Straight genetic fact. Genetic diversity of people with recent ancestry in Africa is far greater than the rest of the world put together.
Of course those that believe in "purity" being a good thing are witlessly ignorant of basic science.
As any fule wot has done basic genetics knows that "Pure" in this context means pretty much the same as "a bit inbred". Populations with low genetic diversity are inherently unstable and vulnerable to plagues.
As it happens I come from one of the "purer" white populations (Irish). We are whiter than most poeple who would refer to themselves as white. That's a function of being on the edge of Europe and living in a rainy place for too long; rarely do people think of the Irish as a dominant elite.