Radical feminists believe that feminism is by, for, and about females, regardless of gender identity or presentation. And that males, regardless of gender identity or presentation, can be allies and supporters but not active members of the movement. This isn't trans exclusionary; there are many trans women who are radical feminist allies (snowflakeespecial and atranspaige, among them), and many trans men as well (including me, but I prefer my anonymity).
Imagine there were a set of public toilets. If trans people were not allowed in, that would be trans-exclusionary. That’s a rarer situation; more often what happens is that trans men are told that they must use the ladies, and trans women are told that they must use the gents.
When women’s spaces are inclusive of trans men and not trans women, and men’s spaces are inclusive of trans women and not trans men, this is trans-exclusionary.
And pushing for one thing does put pressure to prevent the alternative; when you expect to get into women’s spaces as a trans man, that is increasing pressure to exclude trans women from there, and to exclude trans men from men’s spaces.
by, for, and about females, regardless of gender identity or presentation
In other words, transition no real. However a trans man ~feels~ or ~presents~, no matter how many male pronouns he accessorises himself with, he’ll always be female. He can treat his dysphoria with HRT/surgery, and he can play-act, but he’ll always be female.
There are two ways that you can consider yourself:
You have a medical condition that means, biologically, you were never 100% female. You transition to live as a man (such as relinquishing your claim to women’s spaces), and as long as you pass or are accepted as male, are treated as a man. You change your body so that some sex characteristics that were female are now male.
You were born female, and will remain female. You may feel different, but you can’t change your sex. You are a female with a couple of body modifications.
I go for #1. I was AFAB, but that does not define me. My body is not female, and I do not live in society as a woman. If you go to #2, that is little different from the ‘womyn-born-womyn’ thing.
This form of radical feminism is trans-exclusionary, for the exact same reason as the second toilet scenario I opened with. And it matters - it is damaging hard work done to try and have society view trans women as women and trans men as men. It is undermining my position as a male and a man, and my claim to men’s spaces, so I have every personal reason to speak out against this.