Focusing on income taxes doesn't convey the full picture of the U.S. tax burden. Most low-income individuals who pay no income tax face federal payroll taxes, along with state and local sales taxes.
"It's a fair point if given in context," said Dan Maffei, a former congressman from New York who is now a distinguished senior fellow at Third Way, which develops policy ideas for Democrats. "Frequently, the Republicans don't put it in any context, and often they drop the word 'income'."
Any effort to increase the pool of filers could fall most heavily on those at the bottom of the income scale. This is compounded by efforts to reduce top marginal individual and corporate rates to 25%, as proposed by Representative Dave Camp, chairman of the House Ways and Means Committee, and Representative Paul Ryan, chairman of the House Budget panel.
To hit that target, Ryan and Camp would need to eliminate $2.9 trillion in so-called tax expenditures over the next decade, according to the Tax Policy Center.
The problem, Williams said, stems from the dual mandate that Congress has given the IRS. The agency runs a tax collection system and a benefit distribution system, doling out incentives for energy, housing, health and income support.
'Hybrid System'
"We're mixing apples and oranges in trying to get the IRS to run this hybrid system," Williams said.
Pulling all those functions out of the tax code and turning them into spending programs would make it easier to create a tax code that limits nonpayers to those with very low incomes.
The other approach to increasing the number of federal taxpayers, Bartlett said, would be to impose a federal consumption tax, such as a value-added tax. That would be regressive, too, because low-income individuals tend to spend a greater share of their income than others.
"The more practical problem is simply that we need additional revenue to reduce the deficit," Bartlett said. "It's impractical to think we're going to get that simply by soaking the rich."