The draft recommendations of the president's commission on deficit reduction call for closing popular tax deductions, higher gas taxes and other revenue raisers to drive tax collections up to 21% of GDP from the historical norm of about 18.5%. Another plan, proposed last week by commission member and former Congressional Budget Office director Alice Rivlin, would impose a 6.5% national sales tax on consumers.

The claim here, echoed by endless purveyors of conventional wisdom in Washington, is that these added revenues—potentially...