That's the question millions are asking after reading his column noting that both the Democratic and Republican platforms call for re-instating Glass-Steagall. (It is important to note that the Democrats refer to the 21st Century Glass-Steagall Act introduced by Senator Elizabeth Warren. This measure would also address some of the problems created by the shadow banking system by changing rules on repayment in bankruptcy. This would put a check on the ability of troubled institutions to have access to credit markets.) Sorkin indicates that he doesn't approve of Glass-Steagall.
At one point he tells readers:
"Whether reinstating the law is good idea or not, the short-term implications are decidedly negative: It would most likely mean a loss of jobs as part of a slowdown in lending from the biggest banks.
"There is a reasonable argument to make that it would also put the United States banking industry at a competitive disadvantage relative to international peers, some of which face fewer restrictions."
It would be interesting to know how Sorkin decided that reinstating Glass-Steagall would reduce lending in the economy or even big bank lending. (It is possible that a reduction in big bank lending would be offset by more lending by smaller banks.) The big banks were supposed to keep a strict separation between their investment bank divisions and their commercial bank operations, so it's not obvious why a separation would reduce lending if they had been following the law.
It is also worth noting, that according to standard trade theory, if our surplus on banking services is reduced by a new Glass-Steagall, our trade deficit in other areas, like manufacturing, would decline. Many people might consider this a desirable outcome. Of course, this assumes that people follow the trade theory that ostensibly underlies NAFTA, the TPP, and other recent trade deals.
It is worth noting that Sorkin is right that Glass-Steagall would not have prevented the economic crisis in 2008. The problem was allowing a massive housing bubble to grow unchecked. When house prices collapsed the mortgages, and other assets that depended on house prices, plunged in value. The repeal of Glass-Steagall did not in any obvious way contribute to the bubble.