I think I agree. If you (not "you", exhawg, specifically, but "you", anyone, generically) were born with all the parts of a boy, and at whatever age you decide you're more comfortable claiming to be a girl, fine. Check the box that says "girl". Wear a dress and do all the "girl" things you want to do. And as a girl or a woman or whatever, you want to compete in sports, fine. But we, as a society, need to wake up and see that, even though it isn't politically correct to say this, males and females are different. Our bodies are different and our brains are wired differently. And while there's plenty of women out there who could kick my ass in plenty of physical tests, I'd probably do better against the field of women than I would against the field of men. So while I don't want to tell anyone to not live his/her (or whatever pronouns someone wants to claim) best life, I don't like the idea of taking fair contests and making them unfair.
The rules of swimming or running or any other race is simple: get from here to there as fast as you can. If we agree that men and women are different, we can all agree that men and women should be separated in these types of contests. If we're going to blur the lines in these contests, then maybe we should just combine them all, anyway. Imagine all the women who would happily not have a swim team or a basketball team or a soccer team because we decided that the men's and women's teams should be combined.