Jumping in having only read three pages, because my thoughts have been swirling around this all afternoon.
I used to accept "trans women are women" despite the difference in biology because I understood that the label woman refers to both a biological category and a social category, which generally (but not exclusively because intersex) overlap. I fully accepted the existence of the social category, because men and women are evidently treated very differently socially, and my externally-female friend was very definitely in the woman social category despite not quite meeting the biological requirements. it is therefore possible, I reasoned, to be a woman/female socially yet a man/male biologically.
I weighted the social category as more important than the biological category, because I had been raised to believe that who we are is more important than what we are. I was also keenly aware that my intersex friend was struggling with her identity within the male/female binary society is built around, and I was subconsciously very strongly motivated to comfort her by emphasising our shared membership of the social category while devaluing the importance of the question mark over membership of the biological category.
I can identify all the problems with my younger self's reasoning now - I won't preach to the choir but suffice to say: experiencing first hand, and witnessing in my peers, just how the social category gets utterly shafted when we exercise our membership of the biological category by reproducing, was a hell of a kick up the metaphorical arse.
From these experiences and observations, I inferred that enforced membership of the social category and all that entails - the clothes, the career paths, the caring, all of the other submission-inducing crap that is shoved into the pink box and forced on us from the day we are born - the gender that really IS violently and coercively assigned - is the very mechanism by which women/females are oppressed. And "trans women are women" not because they are in the biological category, not because they are in the social category, but because they are in the "embodying and identifying with the mechanism of oppression" category, and the overlap between that category and the biological category is more commonly known as internalised misogyny. TWAW if, and only if, the defining, unifying feature of woman, that we all share, is internalised misogyny.
And you have to have internalised a metric fuckton of misogyny to define yourself like that.
This makes me particularly angry because I feel my goodwill towards my intersex friend, my urge to comfort and support her and boost her psychologically, my capacity for sisterhood, has been exploited and used to strengthen and legally enshrine the very mechanism by which I and my sisters are oppressed.