Katz is far less sanguine. In a series of email exchanges, he warned that “there are reasons to worry that tax avoidance and international migration and capital flows of the rich could be more important today than in the historical variation they examine. I would certainly be nervous going up to marginal tax rates as high as they suggest and I think even they believe one would need international coordination to do so.”

More conservative economists have examined the issue of inequality and growth and come to very different conclusions from their counterparts on the left.

Robert Barro, a professor of economics at Harvard and a senior fellow at the Hoover Institution, has also studied the relationship between growth and inequality, reaching the conclusion in a 2008 analysis that “a cross-country-growth framework reveals a negative effect from income inequality on economic growth, holding fixed a familiar set of other explanatory variables. This effect of inequality on growth diminishes as per capita G.D.P. rises and may be positive for the richest countries.”

Gregory Mankiw, yet another member of the Harvard economics department, threw down a gauntlet to the left in his now famous — or infamous, depending on your point of view — 2013 essay, “Defending the One Percent.” He writes: “Since the 1970s, average incomes have grown, but the growth has not been uniform across the income distribution. The incomes at the top, especially in the top 1 percent, have grown much faster than average. These high earners have made significant economic contributions, but they have also reaped large gains.”

What, then, should government do?

Mankiw’s answer: nothing: “In the end, I am led to conclude that concern about income inequality, and especially growth in incomes of the top 1 percent, cannot be founded primarily on concern about inefficiency and inequality of opportunity.”

Mankiw mocks liberal thinking on redistribution: “The rich earn higher incomes because they contribute more to society than others do. However, because of diminishing marginal utility, they don’t get much value from their last few dollars of consumption. So we should take some of their income away and give it to less-productive members of society. While this policy would cause the most productive members to work less, shrinking the size of the economic pie, that is a cost we should bear, to some degree, to increase utility for society’s less-productive citizens.”

Economists are deeply polarized on the issue of “optimal inequality,” as well as on optimal top tax rates.