Simon Johnson writes: Earlier this week, Richard Fisher, the president of the Federal Reserve Bank of Dallas, captured the growing political mood with regard to very large banks, observing, “I believe that too-big-to-fail banks are too dangerous to permit.”

Market forces don’t work with the biggest banks at their current sizes, because they have great political power and receive almost unlimited, implicit subsidies in the form of protection against downside risks — particularly in times like these, with Europe’s financial situation looking precarious. Mr. Fisher added:

Downsizing the behemoths over time into institutions that can be prudently managed and regulated across borders is the appropriate policy response. Then, creative destruction can work its wonders in the financial sector, just as it does elsewhere in our economy.

Mr. Fisher is a senior public official and also someone with a great deal of experience in financial markets, including running his own funds-management company. I increasingly meet leading figures in the financial sector who share Mr. Fisher’s views, at least in private.