Here's the relevant section from Ross Tucker on the "Phelps" analogy.
Whilst I agree with all the points I find section 4 the most powerful in that it not only explains the reason for sex segregation but the impact of not upholding it by referencing the scale of male physical advantage.
"Another problematic argument in this area of concept is the notion that having a high T value is a natural advantage, and should thus be ignored, because after all, we don’t regulate things like height in basketball or foot size and arm length in swimming. I’ve seen academics make this argument, and I don’t agree with it. I want to talk briefly about why this is problematic, and ultimately, possibly damaging to the sport, if these people were to win their case:
1 First, we don’t compete in categories of short people in basketball or people with small feet and short arms in swimming. This is important, because our decision NOT to “protect” the people with these “disadvantages” means that we don’t need to concern ourselves with things like feet size or arm length. It’s irrelevant. If we decided to police foot size in swimmers, maybe it would become relevant.
2 But, and here’s the thing, we HAVE decided to protect the competitive integrity of women’s sport. We do this because we understand that in two athletes who are equal in every respect except for biological sex, the effects of testosterone in the biological male create such a large disadvantage for the athlete without those effects (biological female), that they would vanish from sport altogether. Thus, having drawn a line, we must defend the line.
3 Perhaps one can make a reasonable argument that we SHOULD defend a line of height in basketball – short people, below 1.81m. But then, someone who is 1.815m tall can’t play down. That would be easy to do because height is easy to measure. Sex unfortunately is not, but the point remains, we decide somewhat arbitrarily to create categories.
4 I also reject this comparison because I guarantee you that having small feet or short arms is not as much of a disadvantage as having no benefit from testosterone. In other words, these “disadvantages” are not equal in size to that of being female in sport. If all things are equal except for Variable A, then the person with smaller feet is not going to be 4000th in the world rankings for humans. But when all things are normal except for Testosterone, that person would be.
5 Qualitatively and quantitively, then, testosterone differs from these commonly used arguments. I don’t know where I’d put things like muscle fiber type in this conversation – it may have the same effect size as “androgenization” due to high T, but I don’t know. Regardless, it’s moot because again, we don’t have an Olympic champion for “slow-twich muscles under 60%” and another for “fast-twitch muscles over 60%”. If we created that category for those slow-pokes, then we’d have to concern ourselves with this argument
6 Finally, this argument that says “Don’t regulate natural advantages” ends in a disaster for women’s sport. Why? Because being “male” is a natural genetic advantage! It may be the greatest of them all! If you have the Y chromosome, and the testes, and the testosterone, and you can use the testosterone, then you have a huge advantage compared to a woman who has all the same other attributes, but not those. So if you really want to get rid of regulation and separation based on “natural genetic advantages”, then you should just as well throw all humans into one race, and crown the “World’s fastest human”, and see how women get on."