If I was nitpicky, I didn’t mean to be… I took “extinct” to mean “gone” rather than “changed-over-time” or “combined-with-others”; and I was answering the question as if the concept-of-race or the concept-of-division were gone, rather than a section of humanity or sections of human culture were suddenly extinguished. Having a potentially divisive concept gone is much less problematic than having actual humanity gone. My answer would be more or less the same if the word “race” was swapped with “ethnicity,” though I would change a few things.
From my understanding, race as a concept has historically been tied to ideas of power and superiority, of one group trying to cement their dominance by claiming their blood/intellect/etc. was better than another group. Ethnicity, from what I understand, is our more recent attempt to tie social identities back to cultures rather than bloodlines. And while it doesn’t have the same hierarchical connotation, it still tends to follow racial lines, and insofar as it does that, it makes me a little wary. Insofar as it celebrates our remarkable cultural diversity, I am more comfortable with it. Still, ethnicity would be a social construct of distinction, and consequently even as it tries to recognize diversity it may add artificial separation between groups. The fewer conceptual divisions we place between each other, the better, I think. (Or I hope?)
But if we’re talking about a gradual combination or assimilation, I think of it less as extinction and more as evolution. (Perhaps I am being nitpicky…)
Considering the cultural aspect ethnicity brings in complicates the issues. Combination often means giving up certain aspects of one, and certain aspects of another (which in itself isn’t necessarily bad, but the majority-ethnicity often expects the minority one to give up more.)
As far as the physical differences we have—some random mutations causing things like blue eyes, and some ten-thousands years separation where humans at different latitudes lost various amounts melanin pigmentation because they needed less protection from the sun and more efficient vitamin D production… I’m not so concerned about those becoming blended. Even if our hair and skin hues do begin to converge on a single shade: we’ll still be able to perceive wide differences between each other (we learn as babies how to attend to differences to distinguish people); there will still be recessive traits carried through the genome that will emerge; we’ll still decorate ourselves with fashion/style/art; and our faces, bodies, postures, and personalities will still be unique, etc.