I see where you're coming from but that doesn't really refute the idea for me... Some cultures didn't develop footbinding, but that doesn't disqualify footbinding as what it is.

And even if they arose purely for convenience, why did they stick around? If today's populations really developed the self-reflection to operate critical of importance of sex, why are "he/his" not as weird to say as "whitey/whitey's" would be as pronouns?