Bearing this in mind, we should start thinking of a two-parent upbringing as something to which children have a right. Helpless infancy and growing up are as much parts of human nature as anything else. The necessary flip-side of this coin is that parents have a responsibility to their children.

This isn’t an absolute right that overrides all others. If one philanderer impregnates two women within the span of a month, that would be a wrong thing to have happened. What happens next is less clear because the ideal outcome is already ruled out. Of course, promoting the cultural expectation that people have a responsibility to raise their children minimizes this outcome in the first place.

The ways this understanding would manifest in public policy are as disparate and subtle as our legal code itself. It might at least result in an end to state-sponsored payments for birth parents to stay apart, even if that’s just the unintended consequence of a good-hearted effort to help single parents. But when we talk about parents and children, we would be more correct not to think of a two-parent upbringing as a privilege to be enjoyed by the rich few — just an accident, occurring apart from human input — but as something every person owes to every other person he or she hazards to create.