Wilkinson takes Santorum's economic plan to task:

Mr Santorum promises to "triple the personal deduction for children and eliminate the marriage tax penalty". What does any of this have to do with economic freedom? If paying people to have children makes them more free, why don't the childless deserve equal freedom? Because freedom is the freedom to do God's will and God wants us to have big families? The "pro-family" elements of Mr Santorum's plan are transparent attempts at social engineering through fiscal policy.

Reihan defends the child tax deduction:

On the whole, I’d rather we subsidize child-rearing than the purchase of large homes in capacity-constrained regions or high-tax jurisdictions at the expense of low-tax jurisdictions. Not subsidizing child-rearing, meanwhile, might deepen the advantages of those, like myself, who delay having children, and thus contribute somewhat less to the building the human capital endowment of the generation that will pay for old-age transfers, etc., than those who do not. 

Wilkinson counters:

If growth is really the justification for government paying people to breed, then people likely to produce kids who will grow up to consume more than they produce ought to pay tax penalties for their precious, pitter-pattering economic dead-weight. Generallypeople more likely to produce growth-enhancing kids should be subsidized more heavily than people who aren't. Pro-growth tax policy ought to especially reward those who produce kids exceedingly high in conscientiousness and IQ, which is to say, tax policy ought to reward people who are themselves very conscientious and highly intelligent. Of course, this sort of Grade A human livestock is likely to do quite well economically without special tax breaks. So perhaps it would be better to reward them medals for fecundity, as the Soviet Union used to do.

Anyway, hardy is the supply-sider who does not break a tooth biting the eugenic bullet. But the logic of the pro-growth argument for the child tax credit really does require biting it.

Wilkinson follows up. Reihan goes another round.