Because we have biological evidence for a sexuality which is richer than his socially-constructed binary sexuality. Specifically, we know about intersex [0] chromosomal arrangements, and we know that they don't just neatly fall into male and female arrangements.

We might expect of university professors that they grok the basis of their field, and what they're actually studying. When somebody insists that they ought to be tenured, we ought to double-check that they understand science. The Nature memo that he complains about [1] merely says that the Trump administration is incorrect to think that genitals determine chromosomal layout, and a brief sanity check shows that indeed it should be entirely the other way around, and even then, chromosomes don't guarantee that genitals will develop a certain way.

The author groks this critique and doubles down; in [2] he insists that intersex people are less than 0.02% of the population, and thus don't matter. That should show you exactly how unscientific he is; he points to his degree over and over as evidence of his quality, but fails at hard numbers. Meanwhile we estimate XXY chromosomes [3] and XXX chromosomes [4] to occur in around 0.1% to 0.2% of the population, and that's just one of dozens of possible chromosomal arrangements. (Or two, I guess, depending on how one counts.) He is at least an order of magnitude off, possibly more, and doesn't care because it would require him to back down from the hill he's chosen.

[0] https://en.wikipedia.org/wiki/Intersex

[1] https://www.nature.com/articles/d41586-018-07238-8

[2] https://quillette.com/2018/11/30/the-new-evolution-deniers/

[3] https://en.wikipedia.org/wiki/Klinefelter_syndrome

[4] https://en.wikipedia.org/wiki/Triple_X_syndrome

> Why should a university professor be cancelled because after his research he says he has evidence that sex is a biological construct and not a social one?

This isn't what happened. It's one thing to author papers and submit them for peer review, it's another to do this:

> I also eventually co-authored another Quillette essay, with endocrinologist Dr. William Malone and author Julia Robertson, titled No One Is Born in ‘The Wrong Body’.

Viewpoints like this are dismissive of trans and gender noncomforming people, and they put minority people in the position of having to constantly advocate for the fact that they do, in fact, exist. He goes on to describe several other instances where he calls, for example, gender dysphoria in Sweden "social contagion".

This person is widely, and publicly outspoken about their beliefs in op eds, and people are disagreeing with his op eds . This isn't a case of "I published some academic papers and people didn't like that", it's "I entered the arena of public opinion with my own editorials that specifically targeted trans and gender nonconforming people and people didn't like that."

I wasn't talking about any particular case, it was just an example...and it happens. Not only with teachers but with anyone who might have an opinion that the mob doesn't agree with.