I often wonder if it's society saying it, or if it's reality (e.g. our biology or plain logic) saying it and our society just echoing. For example, society is saying that you should brush your teeth, but science is also saying that, so it's a good thing that society is echoing and amplifying the message.

For the specific example you mentioned, I think it's very likely that society is just echoing what biology is dictating, which is that men have sex/children with as many women as they can, and women to select as good genes for their few children as they can.