After Mitt Romney was captured on tape last week discussing how 47 percent of American households pay no income taxes, commentators and economists on both the left and right were quick to point that this was to a large degree driven by so-called "refundable tax credits" like the Earned Income Tax Credit (EITC) and Child Tax Credit. These credits have enjoyed a great deal of support among conservatives because they are simple, transparent, and obviate the need for expensive and cumbersome bureaucracies. And on both the left and right, there's a widespread consensus that refundable credits work: liberals like them...