Let me rephrase: not MERELY a biological thing. That is not enough information to define a woman. If that's all it meant, you wouldn't be referring to strangers in public, whose biology you do not know, as "women."

This isn't a new thing. These arguments go back decades. You're just not aware of the literature.

You're arguing about being Black and referring to biological traits. So, the comparison is between race and femaleness, not "woman". You can argue that trans women will never be biologically female. Make that argument.

There is no racial correlative because there's no way for white people to take on the identity of a Black person without them winding up like Rachel Dolezal.

Intersex people do have something to do with trans people. They prove that even something that's biological, that people have thought of as so dichotomous, so easy, is complicated and confusing. And if something biological can be so third-way, and complex, then gender, a totally invented construct, is even more complex.

There isn't anything I said about "woman" being an idea and a construct that isn't coherent. Some people find it really easy to follow along. Other people don't... and don't want to. *shrug*