1) I’ve been trying to work out the philosophical position on trans inclusion in sport of Rachel Mckinnon and I think I have made some progress. Here’s a thread:
2) It’s important to notice that RMs position in favour of trans-inclusion is not, in the end, an empirical or contingent matter. Despite spending some time on empirical data, RM’s position is not constrained by scientific data. It's an in principle position.
3) But it’s important to notice that RM is not against separate classes for men and women. There is a (fairly) respectable position in sport ethics, supported by Tännsjö, Foddy and Savulescu, for assimilation of sex classes. This is not RMs position.
4) There are cases where there is no justification for sex classes in sport: i) equestrian sport ii) target sports (but not archery). We can argue about these...
5) In most other cases, physiological sex differences make it the case that separate categories are fair. If you want to argue that physiological sex differences do not make a difference with respect to sport X, then notice what you are arguing for:
6) you are arguing that sport X is like equestrian sport or like shooting. This is not an argument for trans-inclusion, in sport X or anywhere else.
7) RM separates out the question of sex classes in sport from the question of trans-inclusion/exclusion (TI/TE) RM thinks that Rawls’ Original Position applies to the question of TI/TE. But that can’t be quite right.

There are a lot of side reasons for thinking this use of Rawls is mistaken (below) but here is the main one:
9) The justification of sex classes must be prior to the question of TI or TE policies. Persons in the OP must know facts about human biology in order to know about the justification of sex classes.
10) (see TJ 119: persons in the OP are “presumed to know whatever general facts affect the choice of the principles of justice”
11) If sex classes are justified, they are justified only on the basis of physiological facts about humans. Tännsjö et. Al. deny that they are justified. I think they are justified – and would be established in the original position on the basis of physiological general facts
12) Either RM thinks sex classes are justified, or she doesn’t. If she doesn’t then she is an assimilationist along the lines of Tännsjö. TI/TE policies are irrelevant.
13) If sex classes are justified on the basis of physiological facts about humans then those facts are facts about the performance differentials between males and females.
14) If they are justified in this way, TI/TE policies are also irrelevant, because the physiological difference rule them out. Remember, sex classes are justified, because of physiological differences.
15) RMs view that TI/TE policies can be decided in the OP is mistaken. Illicitly, it ignores the prior question which is whether sex classes are justified.
16) Careful readers of Rawls will notice that there is a lot left out here. RM’s account is open to the ‘basic structure objection,’ ignores the idea that POPs act from a ‘sense of justice,’ or bear the ‘strains of commitment’, or are subject to a ‘stability condition.’
17) But this is enough to be going on with.
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It’s important for athletes and others to come out against RMs rhetoric. Please don’t think that there is some clever radical philosophical argument behind it, which somehow shows that trans-inclusion is fair. It isn't. There isn’t.
19) In the interests of philosophical consistency, of course, RM should adopt and campaign for an assimilationist position, like that of Tännsjö. All the best with that.