There's no need to falsify claims about gender. Gender is a non-scientific cultural category. If that alone suffices for you to eliminate gender, then you accept no alternative to science, thus you submit to scientism. And scientism is a non-starter for me, and most people who believe in gender.
Why would it ever matter that no one can prove me wrong when I identify as male? If I identify as heterosexual, would you try to prove that I don't actually like women? Even a virgin can still claim he likes women and no one can dispute that he has that preference. We don't need to be right about someone's gender, we need to trust that person and their self-identifications. Anything less amounts to disrespect.
Gender is intersubjective, not objective or subjective. A person counts as a member of their gender only if other people accept that they exhibit behaviors definitive of their gender. It makes no sense to say someone is wrong about their gender identifications. The most you can say is that you don't accept their identity. And when everyone else accepts a person as say, a transgender woman, but you reject them as such, we have reason to believe you're just disrespecting that person and distrusting them to further your political ends. Gender is a social construct, and thus, a matter of persons, not facts. If you refuse to accept who a person is when they show you, authentically who they are, you're just disrespectful.