Buffy - when you wrote "or the idea of gender as innate will be dominant, and supported by neuroscientific studies designed to demonstrate this, in the way that other social forces like racism and sexism have been, in the past 'proved' by scientific studies." That's the crux of the matter, and what makes it scary. (I used to joke with my students that if they wanted a one-sentence sound-bite, it was that in essence Bacon said "knowledge gives you power", Foucault says "power lets you define what counts as knowledge".)
But fortunately I think there is a very powerful counterforce to social construction of this brave new world, and that's actually sexual attraction, hence the wider implications of the "cotton ceiling" than simply its rapey overtones. I'm afraid I'm going to be lazy and C&P what I put on another thread:
even if one were to concede your claim that the cotton ceiling is a political issue rather than a personal one (which I don't: I have read enough first person accounts by trans activists to know that they want to pester lesbians into having sex with them) it is still problematic.
Excuse me if I cast this in terms of MTT because I'm heterosexual. Suppose the younger me, aged about 30, is clubbing and starts to make out with a good looking, if rather slender and androgynous looking bloke. We go home together. It gets to the point of taking trousers and pants off. I am confronted with a vulva. Is my reaction:
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that's of no more relevance than the issue of finding a penis which might or might not be circumcised - genitals come in all sorts of external appearances;
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Hell no, that's not what I signed up for here;
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Oh god, my instinctive reaction is no, but that makes me a transphobe, oh god I'm a bad person?
My feeling is a tiny minority might genuinely feel (1). Well over 90% of us would feel (2). Even understood as a political claim rather than a personal one, the cotton ceiling rhetoric is a concerted attempt at social engineer designed to try to gas light as many women as possible in that 90% plus into feeling (3) rather than (2).
So even understood as a political claim, it's still fucking offensive. (And it also shows why trans activists are so keen on the idea - because the fact that most of the human race's sexuality leads them to think along the lines of (2) when confronted with an unexpected vulva or penis when they were expecting the opposite is precisely why actually the whole idea that transwomen are women in every important sense of the word is such an obvious crock of shit - the emperor really has no clothes on).
Adding a bit to that, I'd say that's why social construction will flounder on this one - while I'd be the first to admit there's a huge socially constructed part to sexuality, there's also a massive biological imperative there too - and on that level, you just aren't going to persuade most of the population that genitals don't matter.