The obligation towards childbearing -- and just the bearing of children, not the social and economic rearing thereof -- as a primary moral virtue is to my mind one of the strangest results of the social structures in which we so often find ourselves. Endless reproduction as a chief moral virtue? That's not how you get a human society, that's how you get a Von Neumann machine, and I'd rather not see us becoming the moral and ethical equivalent of a paperclip maximizer.