This topic reminds me of a conversation reported to have taken place between a French missionary and a member of the Nez Perce Indian tribe a few hundred years ago. The missionary was chiding the other man for the immorality of the tribeswomen, who were able to take lovers if they wished. The missionary pointed out that the men of the tribe had no way of knowing if their supposed children were their own. The Nez Perce replied scornfully, "You white men love only your own children, but we love all the children of the tribe".

There actually have been social arrangements that took into account that men don't necessarily know who their children's biological father is- for instance, matrilineal societies where inheritance is through the female line and a woman's brother,not her husband, manages the money and is the male guardian of her children. I don't know that we'd want to replace our own family system with an older one, but it sure wouldn't hurt children if we spread around more of the spirit of loving all the children of the tribe. Sounds like we might as well.