> "Benefit society as a whole" sounds good in theory but rarely works in practice because people are inherently self-interested

This is a very immature POV, IMO. Self interest can, and arguably _should_, be aligned with the benefit to society. That is, in fact, the only way to get _reliable_ benefit to society in the first place. Nobody gets anywhere by trying to piss up a rope. In any situation, you get the behavior you reward. So "self interest" is a good thing, when it's properly aligned to the broader whole.

And if we were to strictly worry about "benefit to society" then one could argue that childless people should earn less, since their amortized value to society in the long term is much lower than that of parents.