(CCing my Ovarit response here!)

So here's the thing with this argument:

If all girls are SO different because we have... different heights, freckles, whatever...

Then why was 'girl' a category in the first place?

Why did we round up half of humanity, across every culture in the world, and say "this is a girl type" and "this is a boy type"?

And why, if trans(male) is just another sub-type of girl (that we're unfairly excluding), why do we not see cultures around the world that exclude other sub-types? Why aren't there cultures where tall girls are treated, socially, as boys? Or flat-chested girls? Or why, in any culture around the world, isn't the 'freckled' sub-type its own gender?

That doesn't happen because 'girl' is not a cultural identity, it's a physical fact. It may have sub-types but the core category is that these are all female children. The fact this cartoon is calling them girls and not PEOPLE in the first place is because they have all have something in common (being female) that not all people share.

If these categories were meaningless, we wouldn't have them across thousands of cultures and millions of years of humanity