Sex is not a social construct. It is a biological fact. It doesn't matter how a person feels about it.
There's a good "how fucked is society" vignette for an SF story: the NOAA (or a similar body) proudly christening their latest research ship the Trofim Lysenko.
Trofim Lysenko, just in case you don't know who he was. (And that picture--holy crap, he looks like the mad scientist from a bad 1950s sci-fi horror film.)
Lysenko eventually ended up being discredited in the USSR, but Lysenkoism is alive and well to this day, and not just in the transgender movement, but in climatology as well. The same motivation applies: giving credence to something which is not the case, solely because it's politically correct. By claiming that a person's sex is a matter of opinion, and that opinion trumps the biological fact of that person's sex, they are effectively stating that reality is subjective. It's not.
Lysenko's work in the early 20th century demonstrates how being wrong in science works. He tried to make people more cold-resistant by dunking them in ice water; all he ended up doing was giving people hypothermia. Any acclimatization his victims managed to cold temperatures was a personal trait, not something heritable, and there was no way that subjecting people to adverse environmental conditions could ever result in a breed of human which was resistant to those conditions. That's not how evolution works; and so every time he conducted an experiment, it failed, regardless of whether or not all his subordinates agreed that it should not have.
The Wright Brothers, before they could build a successful airplane, needed to build a wind tunnel and test airfoil designs, because the airfoil they used--that everyone else was using--turned out to be the wrong shape. Reality didn't care that everyone agreed this was the design to use, didn't care about the concensus of human opinion; reality demanded a different shape, one the Wright brothers developed from experimentation and observation.
And physicists everywhere were confident that the luminiferous aether existed...until Michaelson and Morely inadvertently proved it didn't. Their experiment was designed to detect it, to measure Earth's speed through it--they designed the instrument with the expectation that the aether existed--but no matter how they turned the thing, the interference pattern never changed. Reality did not care about the concensus in the physics community; their theory was wrong.
Concensus is meaningless in science. If a billion people all agree that the sun is a giant bonfire, it doesn't make them right; it makes them ignorant of reality.