Is There a Danger In Restoring Glass-Steagall?

Last week, Gary Cohn, the former Goldman Sachs executive who is the head of Trump's National Economic Council and, supposedly, a figure of growing influence in the Administration, told a group of senators that he's open to reviving the Glass-Steagall Act, the 1933 law that separated commercial and investment banking. This was played as a man-bites-dog story. The dismantling of that separation was raised as one suspect in the 2008 financial crisis, and its restoration has been mainly a cause of the left: Bernie Sanders and Elizabeth Warren are vocal supporters. What was a Wall Street guy like Cohn doing agreeing with them?