The E.I.T.C. may be better than conventional social welfare programs in the conservative view, but it also means that more poor people end up paying no income tax at all. The math is straightforward: If you have a tax situation that would leave you with a $1,000 income tax bill but the E.I.T.C. gives you a $1,000 credit, you end up paying no tax.

That is a major reason that 41 percent of households pay no federal income tax (with some of those, thanks to the E.I.T.C., receiving a refund and in effect paying a negative income tax). Conservatives have increasingly argued over the last decade or two that this creates perverse incentives, allowing poorer Americans to favor more lavish spending without a feeling of skin in the game that comes from having to pay the bill (poor workers generally do pay payroll taxes, it should be added).

“Workers who pay little or no taxes can hardly be expected to care about tax relief for everybody else,” wrote The Wall Street Journal in 2002, in an editorial notable for calling those low-income Americans “lucky duckies” for their low tax bills. “They are also that much more detached from recognizing the costs of government.”

This is also the nub of Mr. Romney’s polarizing comments to donors in advance of the 2012 election. “These are people who pay no income tax,” he said, referring to people who were set to vote for President Obama. “Forty-seven percent of Americans pay no income tax. So our message of low taxes doesn’t connect.” He added: “So my job is not to worry about those people. I’ll never convince them that they should take personal responsibility and care for their lives.” (The number wasn’t quite right — the Tax Policy Center estimates that it was 42 percent of households that paid no income tax in 2012.)

If Mr. Ryan were to succeed in expanding the E.I.T.C. as he proposes, it would lead to more Americans paying no income tax. It is not a revolutionary policy, and would not by itself radically improve the lives of the working poor. But it is at least something concrete that could put more money in the pockets of low-income, working Americans, even if some of Mr. Ryan’s ideological companions don’t like it.