Robin Hood would not be happy if he happened upon our incredibly top-heavy modern world. But the new campaign to levy a tax on speculative trading would most certainly have him smiling.

The most lavishly paid bank CEO in America, Jamie Dimon of JPMorgan Chase, sashayed back to Capitol Hill last Tuesday for still another congressional hearing on JPMorgan’s billions in speculative trading losses this past spring.

Dimon didn’t have much trouble fending off the few tough questions that came his way from lawmakers on the House Financial Services Committee. But Dimon and his fellow Wall Streeters may have much more trouble handling a new campaign — for taxing financial speculation — that launched the same day Dimon testified.

The goal of this new “Robin Hood” campaign: a tiny tax on the ever-churning financial transactions that have made the Jamie Dimons of our time fabulously wealthy.

This Robin Hood campaign for a financial transaction tax actually began two years ago in the UK and quickly spread to over a dozen other nations. The U.S. branch of the campaign launched last week comes with some high-profile champions.

Actor Mark Ruffalo — a star in the hit film The Avengers — introduced the campaign on Tuesday with a video now bouncing all around the online world.

A follow-up came Thursday, when over 50 top financial industry professionals from around the world endorsed the financial transaction tax notion in a letter to the leaders of the world’s 20 top nations economically.

The volume of global speculative trading, these financial industry experts pointed out, now exceeds — by 70 times — the size of the entire real global economy, the actual goods and services that people use everyday.

This massive speculation endangers the entire world. ...