For me, the two crucial difference between That said I'm fine with others feeling a strong sense of gender identity and identifying as a different gender to their biological sex. Live and let live and all that and what is happening on the ground right now are
- the dominant narrative about trans identities has moved from people living "as if" they were the opposite sex, (which yes, typically did boil down to adopting the social stereotypes plus for some, surgery) to "Trans women are women, trans men are men".
The implications of that are:
Women experience sexism not because they are female and society reacts to their bodies in a certain way regardless of how they may feel themselves as a person, but because they are a certain type of person, a "woman".
A male person's experience of "womanhood" in his imagination while living a life where people react to him as a man is as authoritative as a life lived in a female body and treated from birth as a woman.
There's no material reason for single sex anything unless it's entirely a body-based difference (ie medical or reproductive). So women's sports, education, changing spaces, political representation, employment initiatives, anything being done to address historic social, political, cultural and economic inequalities between women and men must become mixed sex to include males who identity as women as equal and interchangeable with female people.
Surgery or any type of physical transition is not a pre-requisite for a trans identity, because the identity is innate and separate to the body. The penis is only male when attached to a person self-defining as a man. Penises attached to male women are welcome in women's spaces. This means separating women and men no longer protects women from rape because some women can rape others.
Statistics that are intended to show sex-base trends and patterns will now include male statistics. This risks hiding female-specific trends and patterns where female representation is very low (for example sex crimes, political leadership) and male representation is very high.
Any discussion of the systemic impact of biology on women's lives - for example expectations and structures around child rearing and domestic responsibility on our economic power over our lifetimes, our physical ability to defend ourselves against male violence, the narratives structured around our bodies in media and in porn - gets taken out of any discussion about feminism and what women need in our society because "not all women have wombs, not all women have vaginas". Which would be ok if alongside recognising that Women is now a mixed-sex group, we had created a new social group for female people and transferred all the single sex protections and analysis over to it. But we haven't. So TWAW has effectively unnamed and undefined female people as a group despite the undeniable oppression and inequality we have experienced and continue to experience.
- "Trans people are who they say they are" AKA self id
All the above would be ok (ish) if there was some sort of objective test or gateway that had to be passed to be accepted as a trans woman (or man). But there isn't. It's being framed as transphobic to even ask. The narrative on the one hand appropriates DSDs and "science" in the sense of research into non-human sex groups, subtleties within human (mostly secondary) sex indicators and development to claim that innate trans identities are "proved" by science and anyone questioning that is a science-denier, but on the other hand resists any suggestion that there could be an objective way to prove trans identities.
Which in effect means the right to participate in women's opportunities, speak as a representative voice of women, enter women's spaces and define women's experiences belongs to any male who wishes to appropriate it.
And even all of that wouldn't matter if this was just (as it is for men) an academic topic. But through lobbying and the tag-teaming of this very specific narrative about trans people onto LBG rights as trans being some sort of "LGB 2.0", (1) and (2) have become the dominant narrative of trans identity and through that, the definition that is being pushed when equality schemes, laws and charters are being defined. Since women are an oppressed/disadvantaged group, how we are defined in these things matters in a why it does not matter to men.
And that's why it matters.