This is something that really deserves book length instead of blog post length treatment, but I do want to throw in a few thoughts based on this very interesting article about people of African ancestry in Argentina that I saw on Negrophile:
Their disappearance is one of Argentina's most enduring mysteries. In 1810, black residents accounted for about 30 percent of the population of Buenos Aires. By 1887, however, their numbers had plummeted to 1.8 percent.
So where did they go? The answer, it turns out, is nowhere.
. . .
But two new studies are challenging those old notions, using distinct methods: a door-to-door census to determine how many Argentines consider themselves black, and an analysis of DNA samples to detect traces of African ancestry in those who consider themselves white.
The results are only partially compiled, but they suggest that many of the black Argentines did not vanish; they just faded into the mixed-race populace and became lost to demography.
Something similar happened in this country, where lots of people who were considered Black in their hometowns moved to other parts of the country and "passed" in some other territory. Probably a scientific study would show lots of people who think of themselves as "white" Americans actually have some African ancestry, the so called "one drop rule" to the contrary.
That isn't to say that such people "are" Black. It is to point out yet again that race is a social construct, not a biological reality, although obviously some people have less opportunity than others to construct their own racial identity.
And, to get to just one of the many points you could get to from this starting place, this calls into question the whole distinction between "mutable" and "immutable" characteristics and the idea that while it is wrong to discriminate based on "immutable" characteristics, it is fine to discriminate based on "mutable" ones. So some people get really invested in the idea, for example, that homosexuality is an "immutable" characteristic. Undoubtedly that's true for some people, but does that make it OK for the government to exert pressure for people to choose heterosexuality if they have a choice? Would it be OK for the government to say that those who are capable of "passing" as white must do so? Seems to me the better argument is that whether a characteristic is "immutable" does not matter -- what matters is that certain personal choices are not legitimate subjects of government intervention at all.
It's worth pointing out that we don't have a problem making religion a protected category in antidiscrimination laws, even though obviously people choose their religion. That's a personal choice that the rest of society has no business in, and it is not the only one.