The author is a Reuters columnist. The opinions expressed are his own.

A superb example of a sound rule in law and economics that needs reviving, because it can halt the rampant speculation in derivatives, is the ancient legal principle that gambling debts are not enforceable through court action.

Not so long ago — before casinos, currency and commodities speculation, and credit default swaps became big business — U.S. courts would not enforce gambling debts.

Restoring this principle offers a simple way to shrink the rampant speculation in derivatives that was central to the 2008 meltdown on Wall Street.

Professor Lynn Stout, a deeply principled Republican capitalist who teaches corporate law at the University of California, Los Angeles, raised this issue at a conference where we both spoke about the 2008 Wall Street meltdown.

“Derivatives are gambling,” she said, referring to credit default swaps, at the University of Missouri-Kansas City law school conference on the financial crisis. “They are a zero-sum game in which one side loses the bet and one side wins,” Stout said.