Sandy Weill, the former CEO of Citigroup, became the latest unorthodox figure to endorse the concept of breaking up the mega-banks. Weill joins former and current Federal Reserve regional bank Presidents like Richard Fisher and Thomas Hoenig, as well as several academic conservatives. What’s even more unusual about Weill joining this chorus is the central role he played in overturning the Glass-Steagall reforms. Citigroup, under his leadership, purchased Traveler’s Insurance, and through a protracted negotiation, secured the breaking down of the firewall between investment and commercial banks. Now he wants to build it back up.

In a wide-ranging CNBC interview, Weill suggested investment banks should be split from banks that provide retail and commercial banking services [...]

“Have banks do something that’s not going to risk the taxpayer dollars, that’s not going to be too big to fail,” Weill told CNBC [...]

Weill said he came to his view about banks after seeing the public, regulators and politicians turn against the banking industry.

The world hates bankers right now, he said.

“There is such a feeling among people, among regulators, among the political system all over the world against the banking system, and I don’t think that is going to change so soon,” Weill said.

This is kind of a silly rationale for breaking up the banks, because they’re disliked. It doesn’t get to the core of WHY they’re disliked, because of their reckless and greedy drive for profits made possible by an implicit government guarantee.

Nevertheless, Weill’s voice becomes central to the debate over breaking up the banks. Sen. Sherrod Brown (D-OH), who is carrying legislation that would but a cap on bank size and leverage, jumped at the chance to tout Weill’s endorsement:

Sanford Weill is one of many banking industry experts who have observed that too big to fail is often too big to manage. Allowing Wall Street megabanks to grow so large and over-leveraged that their downfall would send ripples throughout our entire economy isn’t fair to taxpayers and it isn’t fair to mid-sized and community banks who don’t enjoy the implicit guarantee from the Treasury Department that comes with too big to fail status.

I don’t know how many more bank executives and officials will have to flip before we reach a tipping point. So far this is all happening at an institutional and academic level. No current bank CEO is calling for a breakup, you’ll notice. But there’s an undeniable shift in the thinking of at least some of those in Wall Street’s recent past, and that is undeniably progress.