@nepeta
Thank you for your answer, Elaine Fuchs. I think it is more complicated, because once biological sex is detached from 'women and girls', the gender identity approach replaces those terms with 'people' when talking about sex-based oppression, to be inclusive towards trans men and nonbinary people with female bodies (but at the same time erasing embodied female identities altogether).
This de-fangs feminism almost entirely, in my view, because fighting against sex-based oppression does require being able to name its victims.
Sorry it's taken me a while to get back
@nepeta, please forgive the delay.
I think I disagree on a couple of points here:
Broadly, I view feminism as a movement against patriarchal power structures. Women aren't the only group harmed by this, people of all genders suffer from the patriarchy. For example men can be bound to gender roles too, and suffer from toxic expectations of masculinity. I would say in one way or another, everyone is a victim of the patriarchy (or course not all in the same way, or to the same degree).
I think this is a key tenet of intersectional feminism.
In terms of fighting for women's rights in particular, I think that trans women can and should be allies here because of a great shared purpose. Not every cause in the women's rights umbrella even affects every cisgender woman. Consider the crucial fight for bodily autonomy when it comes to abortion rights. This doesn't directly affect cis women who can't become pregnant, but this shouldn't stop them being included in feminist movements, and it doesn't lessen the word "woman" to include them.
I think the specific point you were arguing against was that by making activism more specific (for example advocating for "people who can become pregnant", or "people who menstruate") it would detach it from the word "woman" and make it less effective by virtue of not being attached to the victims, namely women (please correct me if I've misinterpreted you). I suppose the issue is that by using "women" here, we're already including too many people (for example women who can't get pregnant, or women who don't menstruate) and excluding some (trans men and non-binary people who can get pregnant and menstruate). The inclusive language is actually more accurately naming the victims. (There are some subtle points about making sure that the language used is inclusive as well as understandable to the most people, but this is probably a case-by-case issue). Having said that, I would personally still include these specific issues under the broad umbrella of women's rights.
As for your feelings of gender identity (from another post), it's absolutely not my place to argue that you do feel one and I wouldn't dream of that. The flip side is that I think we have to take trans people at their word here, I believe who they say they are, and that transitioning affects their lives in a substantial and positive way.
I think that you'll find you have a lot in common with transgender people when it comes to gender roles and feminist activism. In actually being close friends, I find it hard to imagine a group more critical of the unnecessary burdens gender places on our society.