The Gulf oil spill is having all sorts of nasty consequences well beyond damage to the regional environment and economy. Not least, the resulting political panic seems to be rehabilitating the thoroughly discredited theory of regulation known as the precautionary principle.

This principle holds that government should attempt to prevent any risk—regardless of the costs involved, however minor the benefits and even without understanding what those risks really are. Developed in the late 1960s, this theory served as the intellectual architecture for the Environmental Protection Agency, which is still required to eliminate certain environmental risks no matter how expensive or pointless the effort is.

Meanwhile, Governor Charlie Crist and other Florida politicians want a Gulf drilling ban unto eternity, and the California, Washington and Oregon Senate delegations want one for the West Coast too. “Without a permanent ban on drilling off our shores,” said Dianne Feinstein, “there is no guarantee whatsoever that this will not happen again.”

In other words, the precautionary principle is back with a vengeance. The irony is that the figure most responsible for dismantling its premises, Cass Sunstein, is now a member of the Obama Administration.

Formerly of the University of Chicago and Harvard, and now the regulatory czar in the White House budget office, Mr. Sunstein calls the precautionary principle “incoherent” and “paralyzing,” as he put it in an essay in the journal Daedalus two years ago.

“Precautions cannot be taken against all risks,” Mr. Sunstein elaborated in his 2005 monograph “Laws of Fear,” “not for the important but less interesting reason that resources are limited, but simply because efforts to redress any set of risks might produce risks of their own.”

Mr. Sunstein’s insight is that there are risks on all sides of a question—doing nothing can be dangerous, but acting might be more dangerous—so the only rational way to judge regulation is to quantify the costs and benefits. If the Food and Drug Administration took a harder line in approving new medicines, it might protect the public from a future thalidomide disaster. But it could also deprive the public of cures for disease or expose it to serious peril, like having no recourse in a pandemic.

In a 2002 book, “Risk and Reason,” Mr. Sunstein pointed out that the best way to prevent automobile pollution would be to eliminate the internal combustion engine. Should the EPA ban that too? “If these would be ridiculous conclusions—as I think they would be—it is because the costs of the bans would dwarf the benefits. Pollution prevention is not worthwhile as such; it is worthwhile when it is better, all things considered, than the alternatives.”

All of this puts into context the ex-post-facto claims that government and industry should have done more to avert a low-probability but high-severity event such as the BP disaster. Is a drilling ban better than the alternatives? These would include more imports even though tanker accidents are more common than large oil well blowouts, the last one of which in U.S. waters was 40 years ago. (The Exxon Valdez was relatively minor in the world-wide context.) And they would include severe economic damage to the oil-and-gas business when one in every 10 Americans is out of work.

Mr. Sunstein has rarely been heard in public since he joined the Administration, and his “nudge” philosophy to encourage better choices in no way influenced the health-care bill. Perhaps he’d care to speak up now? With the reinvigoration of the precautionary principle, the country could use a little empiricism