This subject always reminds me of the problem in feminism (thankfully now much diminished) of how to deal with and treat women who were not feminist, or worse, who spoke up against it. I never liked the idea of treating as traitors a fair proportion of the people we claimed to be fighting for (now men who fit that description, they’re obviously fair game). So we had “yes, they’re women, but not our sort of women, so we’ll exclude them”. Now, when we look at feminism and trans women, we get “well they’re not really women, so we’ll exclude them”.
Now I have a slightly skewed viewpoint, I must admit; as a woman, and a trans-woman at that. To many feminists (including me), a trans woman is a woman, and cannot be excluded from anything based on the fact that she’s trans – and if some feminist is uncomfortable with that, that’s their problem. Deal with it. In exactly the same way that if anyone has a problem with trans women, the problem is theirs – not trans women’s.
As any male feminist will testify, you can only go so far as a male feminist – when women want their own space, you don’t belong in it. No matter how ardent you may be, you’re not a woman, and have to bow out on that one. But what we sadly see a lot of nowadays from some feminists (or simply women’s advocates – they’re not the same thing), is the desire to exclude trans women from spaces set up for women – and that’s wrong. Do we really forget so easily where women were a century ago (or less, really)?
An infamous example of discrimination against trans women occurred in my own adopted home state of Michigan, at the Michigan Womyn's Music Festival, when the Festival created a rule that it would only be a space for cisgender females.
This led to protests by trans women and their allies, and a boycott of the Festival by Equality Michigan, the Human Rights Campaign, the Gay & Lesbian Alliance Against Defamation, the National Center for Lesbian Rights (thank you especially), and the National LGBTQ Task Force. The "womyn-born-womyn" intention first came to attention in 1991 when a festival goer called Nancy Burkholder was asked to leave when several women recognised her as a trans woman, and expressed discomfort with her presence. Guess my opinion of them, why don’t you.
See my post SO WHAT IS TERF ANYWAY?