Professor Greg Mankiw points out that the the top 1% of taxpayers paid 40.4% of the total income taxes collected by the federal government. See here.
I don't think we should have a "free lunch" system where millions of Americans have no financial stake in their government. At the same time, with sales taxes increasing, it's hard to argue the middle class and poor are getting a "free lunch."
It would be more fair to see what percentage of all taxes--state, local, and federal--are paid by the top 10% rather than just income taxes. According to the WSJ, the top 1% of earners pay 26% of all federal taxes. See here. Given the income and wealth disparity in this country, the 26% figure does not shock my conscience--in fact, it seems more on the low than the high side. (Update: the income tax is less than half of federal taxes and only one-fifth of taxes at all levels of government.)
Mankiw's cited statistics show that our income taxation system is inefficient and non-diversified. Any entity that relies on such a small percentage of its "customer" base for 40% of its "profits" will soon have problems. Rather than feel sorry for the super-rich, we should realize that income taxes are volatile and inconsistent sources of revenue. By relying on such a volatile source of revenue, the government isn't doing us any favors.
Mankiw's post implicitly contends that the rich have never had it worse--their 40% contribution is "the highest percentage in modern history," he says. This increased burden could mean two things: one, the rich are getting bilked; and/or two, the recession has hit the middle class and poor harder than the rich, so they are getting smaller slices of the income pie and paying less taxes as a result of receiving less income. I'm going with Door #2. I am disappointed that Professor Mankiw--normally a very thorough writer--cited the Tax Foundation's statistics without properly explaining the numbers.
Overall, we should figure out how to get more paying stakeholders into the system so we diversify revenue sources and rely on more recession-resistant revenue streams.
Update: Professor Mankiw points out that "the [tax] data predate the recession." Although the recession is not factored into the tax data, the disparity in tax burden between the rich and others may still be a result of a declining middle class.