Any time you hear anyone tell you that "all economists agree," get out your gun. Unless the question pertains to the shape of the earth, this is almost certainly not true.
It is most definitely not the case that economists agree that Mitt Romney should be paying his current 14.1 percent tax rate or less as Washington Post readers were told by Dylan Matthews today. Matthews rests his case on some arguments in the literature concerning scenarios in which we both look to an infinite future horizon and we have identically situated individuals, meaning that we all have the same wealth and the same opportunity to gain income. When these assumptions are relaxed, the case for preferential treatment of capital income becomes considerably weaker, as argued in a recent Journal of Economic Perspectives article by Peter Diamond and Emmanuel Saez, two of the most prominent public finance economists in the world.
The second point here is probably the more important. If we have some individuals who inherit immense wealth so that they can live entirely off their capital income and other individuals who must work for their income, a policy that subjects capital income tax to a lower rate of taxation than labor income means that we are taxing the rich at a lower rate than the middle class and poor. It is difficult to see how this is either efficient (we are giving disincentives to work for middle class people as a result of a higher than necessary tax rate) or fair.
Furthermore, as a result of having a lower tax rate on capital income than labor income we are giving people an incentive to game the tax code by concealing labor income as capital income. While most workers may not have much opportunity to play such games, higher end workers, such as doctors or lawyers with their own practices would have ample opportunities for such gaming. This is both unfair and leads to a waste of resources as these people employ accountants to rig their books.
In fact, Mitt Romney and his firm Bain Capital were experts at such gaming. They routinely negotiated deals that changed management fees, which would be taxed as normal income, into carried interest which would be taxed at the capital gains tax rate. Few, if any, economists would agree that allowing for such deals is good policy.
Finally, even if economists might in general agree that it makes sense to have a lower tax rate on capital income than labor income, it does not at all follow that they think that Mitt Romney was paying enough in taxes. The article by Diamond and Saez suggests a top marginal tax rate of around 70 percent. In this case, a 50 percent tax rate on capital gains would still provide a substantial benefit to earners of income from capital. That rate would be more than three times the tax rate that Mitt Romney paid on his income.
So when you get your score card out remember to put down that many, perhaps most, economists believe that Mitt Romney should pay more money in taxes. Don't let the Washington Post fool you.