Mostly, I just want my kids to be able to have a fun experience with sports, and I want the same for other people’s kids.The original claim was that human sexual characteristics are binary. The reality is there are exceptions that reveal the plasticity of the biology. It's a fact that the X can impact the phenotypic penetrance of the Y. In genetics, the exceptions almost always prove the rule. That was my original point.
So it moves, somewhat predictably, to "chromosomally normal", by which I imagine you mean chromosome copy number. Does that provide a clean cut bracketing of "fairness" in sport competition? Well, if you want it to, but that is strictly user defined. Not all X's not all Y's, not all autosomes, are created equal with respect to their contribution to a given trait. Take any metric you want. Height for instance-well studied example. Studies of monozygotic twins raised apart, etc, indicate about ~85% of human height is genetically determined, nurture be damned. Youth soccer coaches are intuitive population geneticists. Little U8 Jr. walks up with mom and dad to the tryout and coach places mom and dad on a percentile, halves the difference. Depending on the values of the coach, Little Jr. makes the cut or not, even if they had good moments on the pitch. To the extent that variance in a distribution for an individual trait can be attributed to genetics the overall message is that life is not fair. Take individuals close to the median. Give them their 10,000 hrs. Do they become outliers? Youth sports, sure, but don't go complaining about it to Li-Fraumeni families.
So it seems ironic to me to try and adopt a genetic parameter as a criterion of fairness, when ithe overall message of genetics is that, from a human value standpoint, competitive advantage is intrinsically unfair. That's not a rabbit hole. It is a direct, and, from my perspective, important, extension of the argument. Perhaps that is why sport actually exists in the first place, to provide a means to show that chance and pluck matter despite it all.
Look, I read what you wrote about Alan Turing. I know your heart is in the right place. But dragging genetics into human value framing issues with adjectives like normal and elite (OK that was the other post) leads PDQ to some historically dark terrain.
At the rec level, a trans kid on a youth sports team, like any other kid on a sports team, is a good thing.
As you get closer to college sports, it gets different. All of a sudden, you have tryouts and cuts. It becomes a zero sum game. If Emma has a place, it means that Susie does not.
And, once you make it a zero sum game, fairness really matters. Placing mtf trans athletes in the women’s events is not a fair solution.