Any discussion about rights for transgender people that starts with the roster choices on children’s sports teams is a bullshit discussion. It’s incendiary rhetoric designed to unsettle people who have never engaged with transgender people.
The counter-argument for that should be “do you know how many kids that affects? This is not a serious issue. You know what is? Trans victims of discrimination and hate crimes. That’s what we should be talking about, not some kids’ soccer league.”
Start treating this talking point like the ridiculous corner case that it is and pivot to the real problems.