The absence of a door strikes some people's sensibilities as mingling the capital-C Clean with the capital-U Unclean.

Which, as I think you're hinting, is largely distinct from anybody's actual health

Yes, that's what I think as well.

I'm all in favour of opaque bathroom doors (and none of these stupid vertical slits American have between their public bathroom doors and the walls). But I wouldn't want to pretend it's about hygiene or health.