Brain scans of schizophrenic individuals differ from those of mentally healthy individuals but that doesn't mean that schizophrenia is just something we need to normalize. Thought patterns, even if you term them "structural", are not, strictly speaking, biological.

I haven't seen any compelling evidence for a biological basis (aside from hermaphrodism).

Of course, if you're arguing biology, then the notion that "gender is a social construct" is incorrect. That would help bury the spurious and stupid "what pronoun do you want us to use" arguments or the idea that any mentally well individual can shift gender identity at will.

And EVEN IF you can prove a biological basis, there is still an incredibly high incidence of mental health issues in the transsexual community and that by itself is reason to keep them out of the armed forces.

Furthermore, I don't care if the army spends more on Viagra than it does on plastic surgery for transsexuals. That's not what the army is there for and not what taxpayer dollars should be spent on. For what it's worth, Viagra is correcting a dysfunction so that people can have children, while surgery for transsexuals is mutilating someone so they can feel better about themselves. Why stop at surgery for transsexuals, then? Give any woman in the army a boob job or a butt job if she asks for it. It's no different, and in both cases it's just a waste of money for something people should use their own money to pay for.