If you are a male person with a certain type of brain - perhaps you are empathetic or have an eye for colour - then that's you, and that's an example of a male brain.
Yeah, that's the thing I really don't get as well.
That people could observe, quite rightly, that some of the brains that grow as part male bodies think a way society doesn't expect a man to think, or the way that person thinks men must think, but instead of concluding "oh, I guess men are more varied than we thought" it's all "oh that means you must actually be a women, which must mean we've totally misunderstood what men and women are since the dawn of time"
They never ask themselves why we would even have this idea of men and women in the first place, if it wasn't from observing the different types of body?
Do they really believe that somehow humanity realised a truth that mutually exclusive groups "men" and "women" exist even though the reason to think it, ie the observation of two sexes, is apparently entirely wrong?
And if that's not improbable enough, do they really think it's likely that by some crazy coincidence, society could have been totally wrong about which people are women, yet somehow the women-only provisions like sports, toilets, political movements that were set up based on that misunderstanding are exactly right for the "real" women anyway, so those real women (ie the ones that meet this newly understood, correct identity definition not the old misunderstood body type definition) can just slip right in with nothing else needing to change because of it?