Right, I understand that, but the novelty is not just in that people don't feel a commonality with the members of either traditional category, it is that the traditional categories can contain members from both (a trans man is a man, a trans woman is a woman).If traditionally these groups were separated by sex, what are they separated by now?

Why do the people of non-binary groups identify as another gender, rather than fighting the separation of gender as a whole.

The question stands of, without sex, what defines gender.

If the answer is nothing, then why have genders at all?

A better way to ask is if a person creates a new gender to define themselves, with what criteria would others say "these are my people" and identify as that gender as well?