The gender crank hangup on gender identity is so fascinating like "ohh it was invented by John Money" no it wasn't, the term was coined by Robert J. Stoller. Both of these guys were researching it to try to "fix" trans and intersex people by changing their gender identities. They were your guys.
"But what's the evidence that people have a gender identity? You haven't proven that it exists." Well you see, you could ask the same thing about the notion of having any personality trait at all.
The term was coined to label something that was already being observed, which was that people will have rather strong opinions on what gender they're supposed to be, and sometimes you'll encounter a trans person, whose strong opinion on their own gender is at odds with their birth gender assignment.
In general, the idea that you have to Prove™️ the existence of whatever you're measuring before you can say anything about the measurements is completely backwards. The measurements come first, and then afterward you build the framework to interpret them.
Early sexological studies of gender identity and its development were motivated by trying to ensure it did so "correctly" according to birth gender assignment, by guys like Stoller and Money. As it turns out, you can't do that. Reports of successful methods to change someone's gender identity were backed by a great deal of scientific misconduct, dishonesty, and outright human rights violations.
The complete failure to actually change anyone's gender identity in real life is the basis for the observation that gender identity can't be changed, that "gender identity disorder" as it has been called at times can't be "cured."
The people who first arrived at this conclusion absolutely fucking hated it, because their careers were dependent on finding the "cure," but everything they could think of turned out to do significantly more harm than simply letting people live according to their gender identity.
Over time, these guys have died of old age and slowly started to be replaced by people with enough self-awareness to ask "are we the baddies?" and push for a depathologized framework for the treatment of trans people. This has gone over pretty poorly with self-styled skeptics who were asleep until the scientifically backed conclusion started backing a minority group they don't like.
The thing these pseudo-skepctics slept through in science class, though, is that psychology isn't the only place where you need to tolerate the idea that you'll make observations first, construct a framework, and then look for evidence that contradicts it rather than Proving™️ that the framework is "true".
This approach is also how we discovered every single fundamental particle, is the thing.
Electrons are indisputably a Real Thing That Exists, seeing as we have a bunch of technologies that depend on electron detectors now. The idea of "an electron" was first introduced in the 1880s as a name for the minimum amount of electric charge observed in ions. They didn't "Prove" that they exist, they just named an observation that was already being made.
The proper discovery of the electron is credited to experiments with cathode rays, based on the deflection of those rays by electric fields, and the heating produced by those rays. From that, they calculated the electrons' mass.
There are, to this day, guys who will insist these experiments didn't Prove™️ that electrons are particles. In a very naive and pedantic sense, this is true: The goal was not to Prove™️the particle nature of electrons. Particles were the best-fit model for what was going on with cathode rays. With no better alternative available, particles were ASSUMED, and experiments focused on measuring the properties those particles would have, supposing they were real.
"Measure the properties supposing that it's real" is how research on gender identity has to work, because there isn't going to be a Gender Identity Detector to Prove™️that it exists. The crank objection is that this is some kind of exceptional reach, some highly dubious construction that undermines the whole field of research into trans issues.
That betrays one of two things: Complete ignorance of how basic research works in practice, or a deliberate effort to lie about it. In either case, the objections don't constitute legitimate criticism. They're politically motivated pseudo-skepticism coming from people who refuse to engage with the existing work on the subject, using the playbook of the kind of person who insists that the theory of relativity and the theory of quantum mechanics are "Jewish science" and need to be debunked.
Not surprising, given that the first sexologist to propose that trans people are simply a value-neutral, natural variation in humans was Magnus Hirschfield, a Jewish scientist whose institute was burned down by the Nazis in the 1930s.
