The Republican right is pushing back hard against the 99 percent movement and its focus on the widening chasm between the fortunes of the few at the summit of the income scale and everybody else. Newt Gingrich, who led the field of Republican presidential candidates last week, argued that the concept of the 99 percent versus the 1 percent is “un-American.” His rival Rick Perry, who led the Republican pack in September, answered a question about taxes and inequality by saying “I don’t care about that.”

This indifference is grounded in a proposition that has for decades dominated American debate over redistributive policies like steeper taxes for the rich: that inequality is an expected outcome of economic growth, and that efforts to tamp down inequality would slow growth down. As President Obama said in his speech in Kansas last week, this strain of thought goes back to at least the turn of the last century when “there were people who thought massive inequality and exploitation of people was just the price you pay for progress.”

Why, conservatives ask, would people exert themselves, study more and work harder if they could not reap extra rewards from the effort? Trying to fix inequities would only blunt incentives to work and invest. As Mr. Gingrich put it, “You are not going to get job creation when you engage in class warfare because you have to attack the very people you hope will create jobs.”

This argument is — at best — incomplete. Some inequality may be necessary to encourage investment for growth. But as recent research shows, intense inequality actually stunts growth, making it more difficult for countries to sustain the sort of long economic expansions that have characterized the more prosperous nations of the world.