I came into my understanding through feminist work. In my view the way women are held down in this world is very much based on gender norms and roles and stereotypes:
Women's place is in the kitchen, women are to be help meets, women are to be modest and gate-keep sex which their whole bodies signal, women are emotional, cannot do mathematics or drive, do not have leadership abilities etc. Religious texts say that men are the leaders of women in families etc.
So the antidote to all that is to relax gender norms, roles, and to change sexist stereotypes so that what someone can do is as little constrained by their sex as possible, while still taking into account biological sex where it clearly matters (tricky to agree on, of course, but not the same as an entirely gendered world).
What I read about trans women, in particular, a long time ago, suggested that their goals were the opposite in many ways: They absolutely demanded to have all those gender norms, roles, and stereotypes in place so that they could be seen as women by following them.
This made me uncomfortable, but as they were a tiny minority, I didn't focus on it too much and wanted them to be treated well and without prejudice.
What changed all this was when I realised the enormous differences between the gay-Lesbian fight for rights and the new transgender fight for rights:
The former didn't remove any of my rights at all, but the latter not only removed many of them but also seemed to require a whole new dictionary where all the common words feminism needs for its work would be redefined so that working against sex-based oppression would become almost impossible.
In other words, the trans activist movement (not individual trans people, but the vocal leaders many of whom are not trans themselves) is clearly sexist and does not care about the oppression of women (as exemplified by the status of women and girls in Afghanistan today). That oppression is sex-based, but the TRAs want all words denoting female sex to be erased.
Add to that how my own gender definition, based on inhabiting a female body is no longer allowed to exist, and I do feel erased.