Jerrica makes art on Nostr: I suppose I used "boundary" because it is the closest to a neutral term one could ...

I suppose I used "boundary" because it is the closest to a neutral term one could expect to get? The word certainly has more positive connotations nowadays (so not perfectly neutral, as you said), but a boundary is still a limitation. Contemporary usage implies a limit to space or behavior that is reasonable or even healthy, but also implies that crossing it will have consequences. Many people don't like that, especially those who feel any limit on personal freedom is negative or arbitrary. (Many such people will happily set boundaries that serve their own interests, but I digress.)

GCs and radfems have frequently discussed how much of trans-activism is about treating the boundaries created by sex, mainly those of women, as arbitrary - or even as something that NEEDS to be transgressed upon. Therefore, I think using the word boundary in this situation is, if not perfectly neutral, more compelling.