only ever seen it as a personal choice

Some people say that it is unethical to have children or imply, rather than personal choice, that it is the morally correct choice. For example: the image in this post which describes having children as great hubris.
If the personal choice is only based on finances, I wouldn’t really call it antinatalism. Antinatalism is based on resentment.

I think the fascist angle comes from its proximity to ecofascism ie “we should kill people because humans are the problem”. I don’t see antinatalism as necessarily fascist, but it’s absolutely inspired by the same desperate misanthropic hopelessness that hangs over heads like poisonous clouds. Just a useless philosophy that cannot make the world any better and imagines doing so as impossible.

I know you are /s but I will respond /srs.
The fact that people in support of trans rights often can’t give a satisfying definition of “woman” is certainly not very problematic or even important at all, but it’s a big sticking point for conservatives and it would be nice to have a real answer.

I haven’t tried this on real people yet, but I think that you can use a simple comparison to show that they also can’t simply define identity words. For example, they probably can’t come up with a simple definition of “father” that includes/excludes all the right people. Pester them on this point. Is a sperm donor a father? Is a man who adopts children a father? Is any male caretaker a father? Is a father-in-law a father? Is a step-father a father? Is an absent father a father?
If they end up with a very complicated & unintuitive flowchart definition, ask them: when someone says “as a father, this concerns me” or “I’m not a good father”, what do they actually mean? Are they referring to your definition? or to a vaguely-defined identity that’s really based in feelings and values?
This really easily transitions into talking about gender because then you can ask them to explain what people mean when they say “man up” or “be a man”. Nobody says those things to mean “be a penised adult human”, it’s obviously about feelings and values.