As an egalitarian, I also inherently dislike divisions in competition based on demographic. Here’s my understanding of why they exist (though my stating the justification here doesn’t mean I tacitly agree):

Chess: currently, only about 40 of the 1600 grandmasters are women. To attain a balance, we ought to be encouraging women to play chess. Women-only competitions are a great way to do this. (There are almost no transgender chess grand/masters, so the same logic ought to apply here – I don’t understand any reason other than bigotry to exclude transgender women from such tournaments)

Sports: I think it comes down to a Schelling division. Now sure, there are other genetic advantages, perhaps race or leg length or height or other aspects influence one’s athletic ability too – top basketball players are generally many standard deviations above average height. However, those are spectra – ranges – so there’s no obvious place to split into two categories. There are basically only two obvious, bright-line, ostensibly binary dichotomies that people tend to believe categorize humans: (a) sex, and (b) disabled status (see: paralympics).

Now, imagine there was a genetic allele that causes humans to be 9 feet tall. About half of humans get this allele. Then obviously we’d add a new category for these super-tall humans, just so that less-tall humans would have the option to compete in sports.

Some sports make divisions on a spectrum, like heavy-weight, medium-weight, light-weight boxing and so on. But these are pretty arbitrary, certainly not Schelling points, so it’s less common for sports to use these divisions.

Now, I often find myself thinking, shouldn’t those certain cis men who happen by nature to be less able than a typical woman be permitted in the women’s category? My gut answer is yes – but the problem here is that there’s just no way to measure someone’s natural capacity for ability. There’s no bright-line, Schelling-point way to sort out these less-capable cis men. It sucks.