One of the least plausible objections that bankers raise against new regulations on their activity is that they would be too complicated.
The world of global finance was not so afraid of complexity when inventing assets made of mortgage debts repackaged so many times even the banks didn't know what they were buying. Compared to the toxic derivatives that fuelled the financial crisis, new regulations proposed by President Barack Obama are delightfully simple.
The basic principle is that banks would no longer be able to blur the distinction between their classic retail functions and their capital market speculations. This is often described as the division between "utility" and "casino" banking. The separation was enforced in the US after the 1933 Glass-Steagall act, but gradually abandoned in the 1990s. Now, in essence, Mr Obama wants it back.
The reason is plain. The credit crunch originated on the "casino" side; that is where all the debts were run up, the risks taken, the bonuses paid. But banks got away with it for two reasons. First, they were perceived as reputable institutions fulfilling a social function. That is because of their "utility" operations: holding deposits, making domestic home loans.
Second, the banks' utility functions were so important to individuals and businesses, they were too big to fail. So when the casino part of the bank went bust, its vast web of debt dragged in otherwise healthy parts of the economy. The whole system nearly imploded and the taxpayer had to step in. That must never be allowed to happen again.
In Britain, meanwhile, the government seems torn, keen to satisfy public anger over banker excess but nervous also of attacking the City, alarming investors and spooking markets just when recovery is taking shape. The Conservatives, who don't yet have to face that dilemma, see that Mr Obama's move is good politics and back it. That should be Labour's instinct too. As global consensus builds around the need for tighter regulation, the City's expectation of special treatment looks ever more deluded.
The banks like to claim that their uniquely big contribution to the economy should be a source of pride. But the opposite is true. Britain's inflated financial services sector is not a national champion, it is a liability. The banks are wrong if they think their size should protect them. Thinking they were too big to fail was what got us in this mess in the first place. If they are still so big, all the more reason to cut them down to size.