Ok, now it’s very clear how babies are made. I wasn’t seeing much logic in men being treated like trash at the beginning of the manga while, at the same time, women still had to have intercourse with men in order to have children.
From what I’ve understood of the story so far, at some point there must have been some kind of “war of the sexes,” in which women won and men ended up being used only as slaves and semen producers.