I'm completely chill about people being whatever they want for how they dress and act, but competitive sports is my line. It is impossible to account for all the differences and all the science and surgeries and drugs can't make shorter arms or smaller lungs or wider hips etc. If you used to be male it is completely unfair to allow play in women's competitive sports and any Trans person who thinks they should be able to play anyhow is nothing but a hypocrite for wanting the same rights and privileges everyone else has, while knowingly trying to force your way into a competition that you have an unfair advantage in.
Why are competitive advantages a problem for trans women but not for anyone else? Breanna Stewart (a cis woman) has a wingspan longer than most men taller than her, let alone the women she plays against. Is that unfair? Should we ban her from the WNBA? What about entire groups of people that have biological traits that give them a competitive advantage in certain sports over the rest of world? For example Kenyan and Ethiopian athletes from certain tribes that dominate long distance running in part because of biological advantages. Should we ban them?
And despite the physical advantages they might have, there is little evidence that trans women have some systemic advantage over cis women in sports results. This is a culture war issue fanned by right wing transphobes who hyper focus on a handful of absolute tiny trans women who have done well (out of an already small pool of trans athletes). And the result is that it also negatively harms cis women such as Caster Semenya, Imane Khelif, or even Serena Williams.
Counterpoint: competitive sports should never have been gender-segregated in the first place.
If that happened, then 99% of women couldn't ever play most competitive sports. There would only be men in sports.