Trans women have spaces devoted to themselves only — why can’t “cis” women? There are experiences that are unique to being born and raised as female — including unplanned pregnancies and other issues with the biological parts we call female (endometriosis, fibroids, ovarian cysts), why would trans women even want to be a part of that?
I’m not sure what makes you think we do. Many of us — if given the choice — would like to have been born with bodies that match who we are. That is, bodies with biological parts you refer to as female (I doubt trans men who have some or all of those parts refer to them that way). However, we recognize that we have not, and would have no interest in barging into the conversation about them. When was the last time you encountered a trans woman in a group for women with polycystic ovaries syndrome? Or a teen mother’s support group? For that matter, except as partner or friend offering support, when have you ever seen a cis woman without that condition getting involved in the conversation?
I recognize that a trans woman might be involved as a friend, caregiver, or spouse — or a combination of all of those — in order to give support as well; that is about the only time I can think of tha a trans woman might enter such conversations. Or is your mentioning this just meant to be a straw man argument? The way it is worded, it surely seems like one whether you intended it to be or not.
On the other hand, many trans men have been assigned female at birth and raised female, and some have dealt with the issues you mention (and more, probably). Maybe you would include them because you think they are women, or maybe you would exclude them, too. I don’t know. I’m bringing them up to demonstrate the issues surrounding viewing any gender as just a collection of reproductive organs.