No one is, strictly speaking, born 'with' a gender. A more accurate analogy might be born into gender, since gender is a set of categories and social mores which, whilst only arbitrarily linked to biological sex, are deemed to be recognised conventions of masculine or feminine looks and behaviour. They exist independently of us and they precede our birth. To muddy the waters further, these conventions are both historically and geographically specific. They are ephemeral and shift with time. Feminine standards of the 1920s are not the same as those of today. Gender non-conformity in the 1980s, to cite another example, is recognisably different from that of today, and was possibly more freeing as it engaged in often quite creative gender-bending within the clear recognition of biological sex.
I suspect that in some sense gendered expectations have always existed in some form or other, and as long as they have existed there will have been people who have resisted them. What is unprecedented is the assumption that this meant they were 'really' the opposite sex and should therefore be treated legally or medically as belonging to that category; not least of insisting that no conflict of rights and safeguarding exists where it patently does, and that anyone who questions this in any way whatsoever should be forced to conform or else be threatened, sidelined, or lose their livelihoods.
As an ideology, gender to the exclusion of sex is regressive. It merely sticks a new label onto an old way of being, but imposes a good many more restrictions onto what that mode of being entails, not least as to how other people living in society should bend their own identities in order to hold up those stereotypes.
That's what is wrong with the twentieth-century brand of genderism as opposed to the trans discourses - if they can anachronistically be called such - of the past. I'd really like to see a return to such a position where there is less pressure placed on people, especially children, to conform with these new gendered stereotypes: because unfortunately, conformity is precisely what these demand. There must be a reason as to the high instances of autistic young people who turn to GI, but as to the medical transition of young people, we are only just beginning to see the potential effects of this and Cass is only the thin end of a very potentially dangerous wedge.