> The fact that 1 in a million people is neither a man or a women
the number you are looking for here (ie only ..
conditions in which chromosomal sex is inconsistent with phenotypic sex, or in which the phenotype is not classifiable as either male or female
) is 180 in a million, or some 4,625 or so in a country such as Australia - which does have some real bearing on things such as national passports and why Australia has a three value gender field there ( M | F | X ).
Less strictly, the prevalence of "nondimorphic sexual development" might be as high as 1.7% or 17,000 in a million.
Like a “race”, a “gender” is a social grouping of either identity or ascribed membership that is distinguished by being viewed as being exclusive with (though, in some models, admitting mixtures as their own unique possibilities), others in the same named group.
> By that definition, isn’t “emo” — or literally any other social category — a gender
No, “emo” is a social category that is not exclusive with genders, its in a different bucket.
But, yes, the distinction of social categories into groups like “gender”, “race”, etc., is, like the categories themselves, fundamentally an arbitrary social construct.
> Do you believe that segregated services — sports, bathrooms, locker rooms, etc — were intended to be segregated by gender, as opposed to sex?
Binary “sex” is just ascribed gender on the basis of a subset of sex traits. To the extent there is a valid basis for segregating services, it varies from service to service. Similarly, the motivations vary from service to service (and, generally differ from the legitimate justifications, if any.)