Well, but my point is that these are two very different statements.

Forcing people into a binary classification socially is probably far more damaging than helpful. It's certainly a lot more damaging than helpful for people who feel strongly that they aren't the class they want to be. It's hard to know whether there are any benefits from a clear binary delineation. (It's not completely out of the question in principle--people do like solidarity, they do like role models "like me", they do like knowing what their purpose is.)

Forcing people into a binary classification medically is also generally damaging--because they'll have trouble getting genuinely appropriate care--unless they don't socially identify as what they medically need to be treated as, in which case forcing them to pick the correct binary class might be important. "I identify as needing prostate cancer screening" could well make the difference between life and death. Men, for instance, have about a 2% chance of dying of prostate cancer. Without screening, the number is more like 4%.

But given that biology is messy, there's little point stating that sex can't be considered unambiguously binary. It's about as binary as it gets. If someone says, "God made 'em man and woman, and that's it, period, end of story," well, okay, it's time for a review: biology is messy! You're going to find exceptions. However, that doesn't mean that there's enough to "rebunk" a spectrum idea. Spectrum is very very very wrong. Far more wrong than binary is. If you want a simple idea, go with dichotomy--that indicates a strong separation, but not literally only two points.

The bottom line is that we can treat people well without having to treat biology with intellectual dishonesty, and we can also understand that we have an awful lot of flexibility to shape our social expectations regardless of biology. Indeed, it is our biology--brains, mostly--which give us that flexibility.