David Leonhardt :
In finance, trading volumes have boomed in recent decades, yet it is unclear how much all the activity has lifted living standards. Paul A. Volcker, the former Fed chairman, has mischievously said that the only useful recent financial innovation was the automated teller machine. Critics like Mr. Volcker argue that much of modern finance amounts to arbitrage, in which technology and globalization have allowed traders to profit from being the first to notice small price differences.
IN the process, Wall Street has captured a growing share of the world’s economic pie — thereby increasing inequality — without doing much to expand the pie. It may even have shrunk the pie, given that a new International Monetary Fund analysis found that higher inequality leads to slower economic growth.