I've said it before, and I'll say it again: it isn't the signifiers, it's what they signify. OK, I haven't said that before in so many words, but it is the underlying theme in all of my work. The problem is the binary. Humans seem to love catagorical thinking and the gender binary is one of the most powerful set of sorting boxes we have.
The problem is that the boy-girl binary has no basis in science. Even if you only sort babies by their outsides, some will end up as "other". If you add in chromosomal or hormonal analysis, the binary falls apart.
So why reinforce it? Why ENFORCE it? Because doing so is cute/fun/harmless/traditional?
As this article clearly shows, enforcing the binary is far from harmless. For the thousands of intersex individuals surgically reassigned as infants, insinuating on either-or was devastating. It's time to bury the binary.