Ramesh Ponnuru makes a good point over at the Corner:
Of course, almost everyone does pay taxes, if you include sales taxes and payroll deductions for Social Security and Medicare. And as Ponnuru points out, "the distinction between income taxes and payroll taxes" probably doesn't strike the people who pay them as deeply meaningful.
It's also worth pointing out that the argument "that it is important, as a matter of both morals and civics, for everyone to pay taxes" is wildly ahistorical. Here's a useful summary from a National Bureau of Economic Research study, "The Personal Exemptions in the Income Tax":
Until World War II, the personal exemptions in this country functioned primarily to exclude most persons and the greater part of personal income from the income tax. Less than 5 per cent of the population, including taxpayers and their dependents, and less than one-third of the total amount of adjusted gross income were covered by taxable returns in most years prior to 1941. . . . The income tax was transformed during and after World War II into a mass tax of unrivaled revenue yield by radically reduced levels of personal exemptions, an accompanying great rise in personal incomes (in part from inflation), and drastically increased tax rates, particularly in the lower brackets.