Is the tax system in the United States fair? That’s kind of a trick question, as fairness and unfairness are usually in the eye of the beholder. Often, a case for fairness boils down to nothing more than self interest. And because there is no final word on the subject, the debate can go on forever. In the current round, Washington is wrangling over President Barack Obama’s call for a “Buffett Rule” to make sure the wealthy pay a “fair share” of taxes — a percentage of income at least as large as that paid by the middle class. Obama says the rule, named for Warren Buffett, the legendary investor who heads Berkshire Hathaway, would raise additional revenue to help reduce the federal budget deficit, expected to be $1.3 trillion this year. “I will veto any bill that changes benefits for those who rely on Medicare but does not raise serious revenues by asking the wealthiest Americans or biggest corporations to pay their fair share,” Obama said.…