I know what you mean, Szygy - and it's hard to be 100% articulate about such an irrational subject.
You're point about 'where were all the would-be transwomen in history' is a very good one. The fact that they don't seem to have been there at all adds to my belief that there's a lot of social contagion/fad/fashion involved, but it happens to be one that is very useful for misogyny/sexism/the anti-feminist backlash.
When male homosexuality was legalised in the UK, I don't think there was such a huge rise in the number of men identifying as gay, who had been there all along but were afraid to come out. I think the percentage of lesbians and gays in the UK has stayed fairly steady, it's the A. N. Others who have mushroomed.
I'm not an historian at all, but I am aware of occasions when a symbiosis between two separate events or movements produced, or assisted in the development of, a latent force or phenomenon. Serendipity.
I think we have been living through one of those moments, when a small, pre-existing group, i.e. transexuals, were used as a fulcrum by misogynists to lever anti-women actions and laws. The spirit of liberalism fostered by the women's movement and the lesbian and gay movement, and our reforming achievements, were used as the weight putting pressure on the lever to dislodge women's rights. The polarisation of right and left added to the situation. Social media was the fuel. The Denton's document DENTON’S DOCUMENT – THE GENDER COLLECTION was the instruction manual.
I'm getting my metaphors mixed up I think, but my point is that we have been at a point in history where a number of factors came together to facilitate the constantly re-occurring and constantly changing assault on women's rights.
This time, it took the form of men co-opting our very identity and our words; very devious, and very powerful.