I was pretty open minded on this but we've already done the experiment here. Lia Thomas was a crappy male college swimmer who took all the hormones and transitioned, and then set all kinds of records and won everything as a woman swimmer. I think it's pretty clear that transwomen shouldn't be competing with regular women in endurance based sports like swimming. Don't really care about abstract research when we have a practical example, that's supposed to be how the scientific method works, basing your conclusions on observed reality and not just hypothesizing endlessly.
Ironically this is a misunderstanding of how science works, in that it assumes that Lia Thomas's strong performance is representative of all trans women in sports. The news article posted upthread already presents evidence from actual transfeminine athletes.
I'm aware I'm not convincing anybody (and I'm probably going to regret posting in here since it'll give me alerts for various horrible posts) but the problem with trans sports bans is that they:
- Assume that the fact of aggregate sex differences in various kinds of physical ability means that an individual man/trans women will always be better than a cis woman (note how this discourse always ignores trans men).
- Assume hormone therapies have no effect on individual performance
- Ignore the presence of dramatic biological variation within sexes
On point one, I think we can all think of cis women who are better than some or most cis men at various physical tasks. Again, in the aggregate it's true that cis men tend to be better at this stuff than cis women, but people differ a lot from each other. If we think about men and women's athletic ability as two normal distributions, there's a huge amount of overlap there. If the argument for trans exclusion is that cis women won't get a fair shake against trans women who are from a sex which is stronger (in the aggregate), then that ignores the many AMAB people whose athletic ability is naturally on the lower end of the distribution on the basis of their assigned sex.
On point two, it's just fairly straightforwardly true that hormone therapies influence the bodies of people who are transitioning, in a way which reduces or even removes a gap with cis women. It's pointed out in the article which Scarlet posted upthread. We would expect that this would push trans women closer to cis female performance on various metrics, especially so for younger people's whose puberties aren't extremely different from cis women. If we're allowing potential outlier anecdotes, I'll note that I've definitely become a bit physically weaker in being on hormones, not that I was much of a Charles Atlas type before.
And finally, sports already have a lot of natural biological variation in ability. There are cisgender women who have an extremely strong biological advantage based on their frame, natural hormonal levels, etc. Even if we reject the previous two points, we're still left with the problem that trans sports bans are discriminating against one kind of woman for a (perceived) biological advantage while doing nothing about other kinds of women with a biological advantage.
Of course, that gets to what the core issue is. If you look at opinion polling on various trans related issues, you'll see that there's a gap between what might be termed a "tolerant position" --i.e. 'live and let live' and an "accepting position" -- i.e. trans people are authentically their gender. The former generally gets much more support than the latter, which means that there are a lot of people who think "trans people should be allowed to live a dignified life, but it's a bit weird and I'm still seeing them as a woman/man." Speaking personally, the fact that that the tolerant position is a decent majority of Americans is a win for trans people.
But the right sees that too, and so seizing onto the sports issue, where assigned sex is so salient, is a way of pushing people in that "tolerant but not accepting" bucket into a viewpoint where they'll be more open to increasingly hostile anti-trans rhetoric. Trans sports bans have been the first step along a path of anti-trans legislation all around the country.
