Your 'fact' isn't factual though. For starters, there are people...

Your 'fact' isn't factual though. For starters, there are people with XXY chromosomes, and for seconds some people have an androgen insensitivity which loosely makes an XY (typically male) individual largely immune to testosterone, meaning they develop typically female external genitalia / traits.

The two binary tests you mention - 'drop the pants' (check their genitals) and check their chromosomes would give opposite gender results in this case (genitals would indicate typically female, chromosomes would indicate typically male). There is nothing wrong with these people, they are just different in one way from most people, and their sex not clearly binary.

So objectively the fact is that gender is not binary, even physically - and there's no one physical characteristic that can conclusively determine it. Biologically it's more like a matrix of characteristics, (and sociologically it's arguably even more complex).

Doesn't have a lot to do with IVZ, but probably about as much as arguing what '2-3 days' means for 3 pages, and more interesting