@BertieFigueres @peter_ellis @gwynnion
"naturally born women" is a category humans invented, not something that
exists. a human is a mass of trillions of fighting animalcules, and like any
such complex system exhibits spontaneous variety impossible to cleanly
categorise. in practice this means that sports are never fair, always dominated
by the few people whose one-off fluke bodies are best attuned to the sport in
question (and that some mutant people like me, though we loved highschool
sports and played anyways, were never able to physically keep up with our
peers). it also means that, even if you don't care about physical advantage, a
separation by "sex" is impossible. a mass of trillions of cells doesn't have "a
sex"; human bodies exhibit variety that straddles every line one could draw,
whether that's alternative receptors or metabolic pathways that aromatise
testosterone into estrogen at higher rates or redirect what would usually be
cortisol into testosterone or prevent testosterone from becoming dht, bodies
with genes atypically methylated or translocated onto different chromosomes to
be active where they otherwise wouldn't be, single bodies with legs composed of
mostly XX cells and arms composed of mostly XY cells (or XXX or XXY or XYY or
XO), organs exposed to atypical environmental hormone levels or hormone
disruptors during development in utero or later, or even spontaneous
duplication or agenesis of certain organs for reasons we often can't yet
explain, this much variety makes any attempt to draw such a line an unavoidably
arbitrary and shifting target that will hurt someone, and your choosing to do
so a value judgement that sees some people as mattering more than others

and even granted you're willing to place some people over others for
"pragmatic" reasons, a ban on trans children in sports still wouldn't make
sense, for many reasons: first that earlier in development girls often grow
larger more quickly than boys do and so can have a size and weight advantage
actually; second because the intersex conditions that make children "trans"
would tend to put them outside the typical physical range of "boys" and "girls"
anyways; third because trans women on hrt typically actually have lower levels
of the "unfair hormone" testosterone than do their cis peers (t levels in trans
men seem to vary much more widely according to their personal preferences),
and, given skeletal muscle has a turnover rate of more than 1% a day, it takes
only a few months to grow a whole new set of muscles under influence of those
hormone levels, which among other factors (including some less obvious, like
heightened rates of joint instability) the supposed on-average competitive
advantages/disadvantages do not pan out

lastly, your suggestion of forming separate "trans-only" leagues is
absurd—there are not enough trans children to form even one full team in such
leagues, and they wouldn't want to anyhow as children hate being differentiated
from and treated as lesser than their peers—and confirms op's original point,
that you either don't care enough about this topic to research or think clearly
about it or your argumentation is a thin mask for simple bigotry