>>Why do I have to show you a human who has gone from producing one type of gamete to another in order to “prove” that sex is not immutable? >>

Because that would be an existence proof. As we're talking about humans, who are physical beings, you need physical proof.

>>To change sex according to this definition wouldn’t require changing the gametes you produce - it would only require changing the body’s “organisation.”>>

That would work, sure. Find us a person who has developed an ovarian artery after previously having a penile artery. Or vice-versa.

>>this idea of “organisation”, which you think is applicable to everyone, even those people who are *manifestly not “organised” to produce gametes*, is a teleological notion and so the definition can be dismissed without further ado as unscientific.>>

Ooh, teleological. And yet we do find that the common factor in all humans is a consistent set of structures, and that variations are caused by definable errors in transcription or embryology. "Organisation" is a convenient way of describing what happens.

>>the preferred term among intersex organisations is “intersex”, and they see “DSD” language as pathologising. It’s best avoided.>>

That's not been my experience from interacting with people online. I do find that people who want to believe (and it is a belief) that sex is mutable (or alternatively "on a spectrum", which sex is not, being binary) want to call people with DSDs "intersex", because that fits their (faulty) belief. It's an inaccurate, misleading, outdated word, and since about 2005 specialists in the field have tried to phase it out. Without success, unfortunately, because some people just won't stop using it.