Should we use taxes to deter financial speculation? Yes, say top British officials, who oversee the City of London, one of the world’s two great banking centers. Other European governments agree — and they’re right.

Paul Krugman

Unfortunately, United States officials — especially Timothy Geithner, the Treasury secretary — are dead set against the proposal. Let’s hope they reconsider: a financial transactions tax is an idea whose time has come.

The dispute began back in August, when Adair Turner, Britain’s top financial regulator, called for a tax on financial transactions as a way to discourage “socially useless” activities. Gordon Brown, the British prime minister, picked up on his proposal,...