I was watching this fascinating video lecture by a neurobiology professor and the brain regions that are dimorphic and are correlated with expressions of male and female gender alignment; but the comments devolved on accusations of "trans medicalism". My assumption is that this is an accusation of boiling down transgenderism to sex-characteristics as expressed through the brain, and the possibility of "testing" that would deny transgenderness if the person doesn't have these correlating sizes previously identified in research.
Am I missing something?
The only way in which it's okay is in providing a clear case for one way (among many others) in which it's valid to be trans. This can be helpful for getting people who might be reachable to go, "oh there's a biological basis and it isn't hurting anyone okay I'll be pro-trans".
This is a limited form of support and can quickly get problematic if someone tries to do more with it. And of course libs do exactly that and it's what trans medicalism is known and rightly criticized for, pigeonholing gender identity into a box that the nerds themselves struggle to even define. The act of trying to tie it down into simplistic categories leads, among other things, to reproducing social constructions that are then claimed to be objective realities. And to also then exclude every other consideration, implicitly or explicitly, despite the fact that basically every trans person will tell you some way in which that's incorrect.
The same approach was used for gay people as well and with similar issues (and a limited positive side). There are people you can get to move away from homophobia through medicalization arguments, like saying someone is born that way so you shouldn't treat it like some kind of choice or "lifestyle" to criticize it. I'm glad this has helped people shed homophobia. But it's also... basically wrong. It's also cool and good to be all kinds of gay/bi/queer even if it's something that develops in you over time, or even deliberately. There are people who have always felt a hard preference/sense of gendered attraction as well as people who have not. There have been many different societal understandings of human sexuality, including what we'd put on the gay spectrum, and that variation in understanding is surely more social than genetic. Folks in my country have gotten gayer over time (which rocks) and it's not because we're a bunch of mutants lol and it's not even just because folks are less closeted. Being able to accept and explore and challenge is also an act of creation - an act of societal co-creation. This also applies to understanding gender.
So while I'm highly critical of medicalization I do give critical support to the fact that a very limited use of it has made some people less transphobic (overall, ironic).