So very odd to insist that the existence of observations that cannot be categorised easily within a strictly binary framework are somehow actually evidence that the variable is strictly binary. Bonkers some of the topsy turvy reasoning on these threads🙃
You're getting confused between a binary system, and phenotypes which can come in a range of physical manifestations that can present in different ways. In fact, everyone including those with DSDs is male or female, but there can of course be more than just two varieties of physical appearance.
That doesn't change the fact that sex itself is binary - it is a system that requires two cells to combine to make a zygote / fertilised cell. There are only two types of cells that can do this and it requires one of each.
Even if a individual animal like a snail is both sexes at once, the sex binary system (sperm must join with egg) remains binary.
The binary sex reproduction system has evolved to aid healthy reproduction. It doesn't give a shit what "identity" someone has or that someone may have atypical features.
Lastly, even if there was such a thing as a person who is neither female nor male, or both, or "cannot be categorised easily within a strictly binary framework" - so what? Why would that imply you can "be" something you're not just by saying so? I'm female. Does the existence of people who may appear ambiguously sexed/have a DSD mean I can decide I'm not female and that becomes true? No. If I say I'm a man, or say I have a DSD when I don't, that's simply appropriating someone else's lived experience.
Lots of things are not a binary - height, age, ethnicity, disability. There's nothing about something being a spectrum or not binary, that means it makes any sense to identify as somewhere on the spectrum that you are demonstrably not.
ETA: 🙃