So, I've had moments in the past where I might have spent 30 seconds thinking about this subject but ultimately I don't give a fuck about competitive sports so my analysis usually ends up being, all competitive sports should be banned because competitive sports are dumb. Which is admittedly a neanderthal take.
But yeah, now the global athletic showdown is going down and seemingly everyone in my immediate vicinity keeps clutching their pearls and I guess I'm sick of not being able to advocate for trans comrades appropriately and articulate a proper response.
So what's a better response besides, "who cares?" Am I missing something? Like, if all things were equitable, what would or should competitions look like?
Help me out. I honestly have no idea.
I hope someone adds to my comment, because I looked into the science part of this a while back and got no clearcut answer, and I'll explain why.
The key question is what is the point of anything. What is the point of a woman's division, and why do trans women threaten that point. Does it matter if trans women would do slightly better than if they competed as untransitioned men, even though trans women are less than 2% of women?
You can't really win with science against the pseudo-science, because it all depends on bigger societal questions for which there aren't objective metrics.
The main arguments they usually use is around trans athletes crowding out cis woman athletes. If an unremarkable male-presenting athlete can become the best woman in the world at a sport, then trans women would crowd out cis women from sport and maybe discourage cis women's participation in sport.
A common point is to imagine an epidemic of mediocre male athletes transitioning to women, where they then steal sponsorship money from cis women. This framing already presupposes a lot of things that are hard to dissect. Like why is it less legitimate for a trans woman to win, why is it stealing? If this is an issue, are there even enough trans women athletes to skew results that much? If it is okay, would it still be okay if every sport's record was held by a trans woman?
The IOC always had arbitrarily decided hormone ranges you needed to be within for at least a few years in order to compete. There hasn't been a transwoman who dominated in anything enough for anyone to have an undeniable argument around adjusting the IOC rules, but they'll pull up random trans people in random sports because there aren't that many trans people in sport.
In some measurements, trans woman lose basically all physical advantages, in others, they retain some advantage even if they aren't anywhere close to the ability they had while male-presenting. The main hypothesis they use is that male puberty is too big of an advantage in most sports even after transitioning later.
To make a definitive statement either way, you'd need to find enough athletes who transition as adults and compare performance percentiles, and maybe how far off the man vs woman records they are after transition. Or have a clearer case of an unremarkable male athlete becoming a remarkable woman athlete.
The most controversial case was that New Zealand weightlifter who used to weightlift as a male junior, quit for a few years, then came back competing as a woman at a pretty old age for weightlifting.
You can't really argue science because on the one hand she didn't win and dominate, and on the other she seems to have placed better as an old woman than as a man in the junior competition (I couldn't find exact records, but she only held the Jr Male New Zealand record, not the Commonwealth games overall Jr Male record).
It all comes down to values and judgment instead of "objectively all world records would be held by trans women" or "objectively every trans woman athlete would place the exact same on hormones that they did as a man".
There are three reasons people will tell you:
To allow people with endocrine systems not dominated by testosterone to play in a sport where testosterone has a large effect on one's capability (or, as the cis would word it: to let women play in a game where men are better)
To allow women to play in a sport without getting harassed by men
To foster female athletes in a sport where men have had decades or centuries of institutional advantage
OK so to the first point, the issue with this is cis people often don't know what they're talking about. For instance, the boxing federation insists on sex chromosomes which has next to nothing to do with secondary sex characteristics. But by now most sports realize it's the hormones that matter. Now, the point of professional sports it seems is to be really good at a sport and break records. People love it when athletes break records, and especially love it when they break the record a lot. Michael Phelps broke a nearly 50 year record on number of first-place finishes for example. Usain Bolt and Michael Phelps still hold a couple records from 15 years ago. Both of their bodies have been studied and had documentaries made about them, and people love to say how genetically lucky they were. So people already accept athletes can be considerably better than anyone else in the world for quite some time. When concern trolling about hormones doesn't work, sports federations who want to ban trans women claim that all trans women athletes will basically instantly be Usain Bolts and Michael Phelps of women's sports. Unfortunately for them, the only female transgender athlete I know of sucked. Another tactic I've seen say World Aquatics use is claiming that sex hormones irreversibly change your bone structure, giving you an unnatural advantage. This is just completely ridiculous. I have seen plenty of cissexual women stockier than me who would be allowed to participate. The actual reason is cissexism: cissexual bodies are natural and allowed; transsexual bodies are unnatural and must be banned and ridiculed.
For the second point, this is plain sexism. Such federations would rather keep their money-making sex pests in rather than foster a safe atmosphere.
The third point is also blatantly incorrect. Skeet shooting used to be integrated. A Chinese woman named Zhang Shan won in 1992. After winning, women were banned from the sport for the 1996 Olympics. Since then it's been segregated. There is a similar story in baseball in the United States. During a minor league baseball game in 1931, female pitcher Jackie Mitchell struck out baseball legends Babe Routh and Lou Gehrig at the age of 17. The day after, the baseball commissioner banned women from the sport. So the actual reason is to obfuscate sex - to make it seem like there are sex differences when there are not. That is, to reinforce patriarchal logic. Interestingly, in their trans-inclusive transgender policy, the ISSF literally admits there is no real reason to segregate by sex. If this third argument was genuine, we would be seeing a move towards integration rather than segregation, and a focus in athletic sciences towards improving female fitness.
Did you know World Aquatics bans all trans women who have had testosterone-based puberty past Tanner 2 after the age of 12, but allows detransitioned women to have been on testosterone for 364 days? I call it the most TERF-coded sports federation.