Here’s the thing about TERFs: The majority define “woman” according to a strict and narrow definition - one which is essentially someone who had a typical white middle-class upbringing or something close to it, was assigned female at birth and raised at least partially according to feminine stereotypes by adults around them, and possesses a uterus. Most of them don’t say this directly, or quite like that, because putting it that way it’s clearly kind of insulting to people who are obviously cis-women but don’t match that definition. A smaller portion would probably define it along the lines of “capable of giving birth, and if you choose to never give birth, you’re denying yourself true womanhood, stop that” either way, that’s how they define their personal identity.
For them, there is no “cis” anything. There is only man, woman, and freak. Intersex people are freaks, albeit ones which are to be pitied, and maybe be considered “honorary” men or women if raised as such. Transgender people who transition are freaks to be despised, because they chose to be freaks on purpose. The very concepts of “trans” and “cis” stomps all over their chosen identities. Meanwhile, their chosen identities stomp all over the chosen identities of not just trans people, but cis-women who define their womanhood differently. And occasionally men as well, when they also define it as an opposition to an idea of “maleness” which doesn’t describe most men.
This is the dark side of identity politics: Any self-chosen identity is very likely to infringe on someone else’s, and to varying degrees. Note that I’m not against it, however. The dark side of lack of identity politics is that the dumbest and most self-serving members of the most dominant subset of society get the biggest say when it comes to defining everyone else. That’s much worse. Note that I’m not excusing TERFs either - if your chosen identity leads you to hate and/or strongly discriminate against others, you really might want to reassess that.
(I suspect that most TERFs would insist that they didn’t “choose” an identity, that’s just how things objectively are. If so, that’s very similar to what “race realists” argue.)