Taxes on the rich and economic growth

A very interesting paper on "Optimal Taxation of Top Labor Incomes: A Tale of Three Elasticities" by Piketty et al. argues that:

"There is a strong correlation between cuts in top tax rates and increases in top 1% income shares since 1975, implying that the overall elasticity is large. But top income share increases have not translated into higher economic growth, consistent with the zero-sum bargaining model. This suggests that the first elasticity is modest in size and that the overall effect comes mostly from the third elasticity. Consequently, socially optimal top tax rates might possibly be much higher than what is commonly assumed."

which in plain English means that (i) cuts in personal taxes in the past thirty years have led to higher income inequality without accelerating economic growth and that (ii) higher personal taxes might not necessarily stymie growth.

Controversial, no?