In comments on my post on Rand Paul and David Letterman, some commenters expressed interest in seeing the data on overall federal tax burden, not just the burden of the federal income tax. As it happens, the Congressional Budget Office reports such data. I would reprint their tables but I haven't yet figured out how to do that. So here is the link for 2006 data. Click on their data and you'll get an Excel spreadsheet that shows the following:
. The bottom quintile paid 4.3 percent of income in taxes,
. The top quintile paid 25.8 percent of income in taxes,
. The top decile paid 27.5 percent of income in taxes,
. The top 5 percent paid 29.0 percent of income in taxes, and
. The top 1 percent paid 31.2 percent of income in taxes.
In other words, it's still the case that the higher your income, the higher a percent of your income you pay in taxes.
So the existence of Social Security, while it reduces the "progressivity" of the tax system, does not come close to reversing it. I would note also, though, that most economists who examine the "progressivity" of the Social Security system also take account of the Social Security benefit formula. This gives a much higher percent of income to low-income people than to high-income people.
Just tossing facts out, there.