but that doesn't prevent these diverse conceptualizations from being particular social constructions.

That doesn't, no. But what I mentioned -- that we have mental programs designed to read cues in our environment that are probabilistically reliable determinants of another's sex -- does.

It seems more than a little tautological to say "there is only one model of sex because all of the other models of sex that people offer are wrong because there is only one proper model of sex."

Except that's not at all what I'm saying. I'm saying "our definition of sex makes sense according to evolution and biology. There are no particularly good reasons, either morally, scientifically, or otherwise (at least given what you've brought up thus far) for why we should want to change it."

But now that I've cited it (and noted that Dr. Fausto-Sterling has a PhD in developmental biology and is a professor of biology at Brown), can we agree that it is in fact a thing proposed by those who have seriously studied biology?

I don't think so, no. I'd have to read the paper, but from a quick google search, of her paper Fausto-Sterling has said, "I had intended to be provocative, but I had also written with tongue firmly in cheek." Besides which, the existence of one such person in the field, whether I know of him/her or not, doesn't make me think it's an idea seriously considered in the field. There are far more climate scientists who deny humanity's affect on climate change.

Thus the question of "what we call racism" doesn't carry the same implications of the question of what we call sex.

But even if you're right, my analogy wasn't comparing the consequences of the meanings of the words....

Consider the fact that legal models of sex in some parts of the United States allow for a person to legally be recognized as a different sex after sex reassignment surgery, but in others states one's legal sex is fixed to the sex one was legally classified as at birth. Thus in some states sex is legally a fixed attribute determined at birth, while in other states sex is legally based on bodily attributes that can be changed by medical procedures.

When you say the word "sex," I assume you mean the biological, scientific definition of the word, the same way I assume by "computer," someone means "a piece of hardware that computes," and not what some country or state has strangely decided to define the sound "computer" by. How a state defines "sex" is quite a different question from what sex actually is.

Simply changing the model of sex would change the outcome (though it's not the only way that we could change the outcome).

You just as well say that "by educating people about what the only model of sex actually is...."

Like I said in my last reply, I used intersex people as an example of how different models of sex reach different conclusions

You keep using this phrase "different models of sex" as though there are actually different models, when there's really only one.... Hence why my inference made sense: given that there's only one model, an example of how we can better treat someone by a different model implies that the only model could be made better.