The ONLY trans woman I have heard speak out against this is Caitlyn Jenner, whom most people agree is kinda trash. And who was an elite athlete pre transition. I'm sure there are others because there's never a consensus on anything.

And it's about it never being right to force trans people to act as their birth gender. Ever.

And there is a huge difference between "You can't make the team because you aren't good enough" and "You can't make the team because we have decided your biology gives you an unfair advantage." That's like telling Michael Phelps he can't swim. And...team sports are also a poor example. Even if a trans girl has an advantage, one trans girl on a team isn't going to immediately turn that team into a powerhouse nobody can beat! Sheesh...

And I assume you meant "No-one is forcing trans girls NOT to compete at all." If somebody is made sick by being treated as their assigned gender, then that is morally equivalent to preventing them from competing. Also, look up what they did to Caster Semenya, a cis woman, because they decided that her testosterone levels gave her an unfair advantage. She was eventually driven out of her sport.