There have always been gender nonconforming males, some of whom live and present as women. In the past, both the language was different and the identity politics were different - I cannot recall any of the people I knew who had male bodies but used female pronouns, etc, who would have dreamed of insisting that they were identical to biological women, or that should have priority access to women's space, or lesbian bodies. If this was still the story, and the whole story, there would be no issue. If all trans women respected both their own identities and women's identities in the way a very small number of trans women now publicly do, at great risk to themselves (hi, Miranda, hi, Helen, and thank you both!) there would be no issue at all.
The issue has changed in recent years, and now is anyone with a male body can steal women's space, women's privacy, women's safety, women's energy and women's resources, just by claiming they are women, and not just women, and identical to biological women, but better than women, and more oppressed than women (I don't know how that works, but apparently it does), despite having male bodies, male socialisation, and every scrap of male privilege they have ever acquired. Some of these people are setting the laws so that women are prevented from doing anything about this, and thus decades of women's liberation work is set back.
This is why in the last decade I have changed my mind on trans issues, and while I do consider some trans women my political comrades and siblings (hi, Miranda, hi, Helen!) because they seek rights and safety for all gender nonconforming people without treading women into the ground, I now cannot consider the mainstream trans movement as anything other than a sexist and homophobic threat to a lot of the successes and hard-won freedoms I hold dear.