So Sex is an Artificial Construct But Race Is Not?

Or at least, if not artificial, fluid, and ultimately dependant on the preference of the individual?
Why is this news?
I thought the world at large had decided we all had to affirm whatever descriptors anyone applied to... oh, I hate for the numbers not to agree, but... themself.
Isn't that how this guy person was allowed to beat the living daylights out of women in MMA?

(I should be upfront about that fact that I find women's MMA disgusting anyway. Actually, I find MMA disgusting, period.)
If Caitlynn Jenner dresses as a woman and the politically correct world is required to honor this choice, (in fact, a bot may chase down those on the internet who use the wrong pronoun for Jenner,) is there any particular reason Ms. Dolezal can't self-identify as black?

Traditionally, one might choose a reductio ad absurdum argument in debate with those whose viewpoints were at odds with ones own, but it seems to me some people on one side of this particular question are supplying one ready made to the opposition.