There’s this phenomenon in this thread where commenters are taking something that’s superficially similar and then making an extreme claim that, upon inspection, does not hold up at all or is completely irrelevant to the argument being made. That is what is happening here. “An adult’s hair color can be different than what it was at birth” is a true statement, but of course is not relevant at all to the claim that one’s gender is just as malleable as one’s hair color, which is what this so-called analogy attempts to do. Real analogies do not do this, and when people deploy the above formulae it’s easy to recognize as bad faith.

Except gender is as malleable as hair color. Sex isn't, but gender is. Gender is the social expectations for a human in the context of a specific culture.

If I live in Virginia until adulthood, then move to American Samoa, my gender expression is going to radically change. I'll start wearing skirts. If I then move to Qatar, my gender expression will change again. I might still think of myself as a man through those changes, but whats expected of me and how I view myself with those cultures will shift. "What does it mean to be a man?" Is very different, globally.

So even if I consider myself a man, that definition regularly changes for different contexts. Clothing, conversational style, physical affection (it's common for men to hold hands in parts of the Middle East, and considered uncomfortable in the states.)

Given gender expression and identity can change as you transit cultures, surely you can see that some people might belong to cultures whose definition of "what does it mean to be a man" might be "whatever the fuck you want". Punk and queer subcultures, for instance, have different gender expectations than say, the Vatican.

For some cultures, genitals have little to no bearing on one's social expectations. Fit into the role that feels right, who cares about what is in your DNA.