Mr. Buffet: IRS Accepts Voluntary Tax Payments
First, Mankiw points out that Buffet's low 17.7% tax rate was because of the 15% maximum tax rate on dividends and capital, which was a large share of Buffet's taxable income, compared to his receptionist, who probably had only ordinary income taxed at the higher rates, and very little dividend income. Further, Mankiw points out that corporate income is subject to double taxation, and Buffet ignored the first round of taxes on corporate profits at rates up to 35% before Mr. Buffet could receive his dividend checks and pay his 15% tax.
Further, if Buffet thinks 30% is a better, more "fair" rate for rich people like himself, he doesn't have to wait for any changes in the tax code, he can simply write a check to the IRS for an additional $5,658,000 to make up the difference between what he actually paid (17.7% tax rate) and what his receptionist paid (30%). He could have done this to set an example, and then encouraged Hilary Clinton and the 600 Wall Street bankers and money managers attending his talk to do the same.