@Radical_EgoCom According to anthropologists, one of the human universals practiced by all cultures is that sex is done in private rather than public. "Realistically," there would probably be other taboos that people wouldn't want to discuss with their neighbors, but might be willing to transact with their dealers.
@Radical_EgoCom As for solidarity, humans are not egoistical homo economicii. But it's a useful approximation. Kin selection promotes familial solidarity... and also sibling rivalry. Imagined communities promote solidarity, but are built on familial concepts, and blood generally trumps religion and nationality. (Imagined communities also have a nasty habit of defining themselves in opposition to The Other.)