The hygiene aspect wouldn't bother me, as I am always clothed, so if I sat down after them there would be no transference of anything unpleasant.
I wouldn't be comfortable with it, but I'm not sure why. I wouldn't be concerned about children seeing (any more than I would be about other adults, that is), as they are just bodies, but something doesn't sit right. I wonder if it's that I am naturally private, so don't stare at people and don't like people staring at me (eg if I see someone famous I would pretend not to notice, as they have a right to a private life), yet it would be hard not to keep looking at them - a bit like when you walk past a house with the lights on in a room right on the street. I'm not sure if that's my objection, but I don't think it should be encouraged.