Greg Mankiw brings a variety of considerations to bear against the Affordable Care Act in a new post, including the idea that it's unfair to transfer financial resources from nonparents to parents:
But having children is more a choice than a random act of nature. People who drive a new Porsche pay more for car insurance than those who drive an old Chevy. We consider that fair because which car you drive is a choice. Why isn't having children viewed in the same way?
Obviously Mankiw has perfectly sound grounds on which to oppose the ACA. Like most conservative economists, Mankiw believes that higher tax rates on wealthy individuals are economically ruinous and perhaps immoral. And the ACA really does include higher tax rates on wealthy individuals. But even though conservative opposition to higher tax rates on wealthy individuals is a well-known and prominent feature of American politics and intellectual life, conservatives seem unable to simply state that this is what's driving their opposition to the ACA. Instead you get this kind of kitchen sink argumentation. But note: Subsidization of child rearing is hardly a unique feature of the Affordable Care Act. Most notably, we spend all this money on public schools! Conservative proposals to replace public schools with vouchers would revolutionize almost everything about the education system in America while specifically retaining the aspect of the system that transfers resources from nonparents to parents.
It is probably possible to justify subsidization of child rearing through some kind of economist-friendly rhetoric about externalities and long-term fiscal sustainability.
But in the real world, I don't think that's even the best way to think about it. (In ecological terms, after all, an additional human being is the ultimate negative externality). One of the main goals of any kind of political community is the enduring of the political community. That requires the rule of law and blah blah blah, but it also obviously requires there to continue to be living, breathing human beings who belong to the political community. Which is to say that children, though expensive, differ from luxury cars in that they are human beings. By the same token, you could note that while it is illegal to take your Porsche ("theft") and also illegal to take your baby ("kidnapping"), we have different words for these crimes and one is punished more severely than the other. Indeed, babies aside, if I were to destroy Mankiw's Porsche, that would be punished much less severely than if I were to destroy Mankiw himself ("murder") because, again, Mankiw is a person. It's not just that people are considered very valuable. Even if I destroyed 10 or 20 Porsches, the punishment would be light compared with if I murdered someone in cold blood. Cars aren't people. Babies aren't luxury consumer goods. That's just how it is.