Okay, but it's not a fact that is remotely obvious in the event that someone is passing and clothed. If you want to identify that person, it helps to know what gender they think themselves to be.
State trooper makes a traffic stop. Compares the driver's ID to the driver. It's not clear to me how "Male, but Femme" or "A dude, might be wearing a dress today" is any more helpful to the cop than "Male".
In fact, I'm hard pressed to think of *any* scenario where it's helpful to me, or to society, to know what gender a person thinks themselves to be.
ETA: Okay, thought of one. If you're a mental health professional considering a diagnosis of gender dysphoria, and accompanying treatment plan, then yes, it's helpful to society to know what your patient is thinking, gender-wise.
On the other hand, society has deemed gender identification to be unhelpful in certain situations. Hiring. Renting or selling a house. Things like that, noticing or caring about someone's gender self-ID is unhelpful.
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And can you imagine Amber Alerts, for example? "Red Toyota Corolla, [LIC], driver is a white male, but be advised he thinks of himself as a woman."
Or even worse: "Driver is a white male, be advised he also identifies as a white male."