so they no longer exist
it seems much harder to imagine a society in which being male or female carries no social meaning whatsoever
I've not seen anyone naive enough to suggest this.
Thinking aloud here, but perhaps a more helpful way of visualising this issue, which is currently being envisioned as two extremes (yours above, and references to problematic stereotypes) - may be a spectrum?
Yes, male and female bodies lead to different social roles. So at one end of the spectrum is the necessary but not sufficient (only women can give birth, but not all women give birth). Amd at the other is the imposition of oppressive and extreme stereotypes.
Where one shades into the other along a complex spectrum that we still don't fully understand - nature and nature etc. - and in any case can only ever be generalised - individuals v. society etc.) will often be subject to debate. This whole discussion is about matters of degree.
And my argument is that there is, currently, an extraordinary and destructive imbalance in this respect, in the societal construction and perception of gender dysphoria and so-called gender identity (indeed, in the very existence of the latter, posters here may argue - most of us are like, Huh? What even is that?!) That imbalance has encouraged reductive stereotyping - I think that's actually hard to argue against (ref. my Barbie > GI Joe post as one example of thousands).
So I think it's understandable that there's real focus on and concern about that in this thread, and to deny its relevance entirely, or to reduce concerns about shades of grey (I point out that even Mrs/Miss/Ms has a problematic history with associated stereotypes - they're often inextricable from your "gendered roles") to the bold above, is perhaps to simplify a more complex issue.