According to this line of thinking, Iran's threats to wipe Israel off the map are not serious. Iran is supposedly not so irrational that it would launch a first nuclear strike against the Jewish state. Surely, the mullahs know what would happen next -- Israel would annihilate Iran. In other words, a nuclear Iran can be contained.
"Deterrence will work with Iran," as General John Abizaid, former Centcom commander and U.S. ambassador to the United Nations, said in 2008. "Despite what their crazy president says, I doubt seriously whether the Iranians are interested in starting a nuclear war."
This may turn out to be a dangerous miscalculation. There is a murderous streak in Iran's public discourse that calls for Israel's destruction and "Death to America." This is also a regime that without hesitation sacrificed thousands of its youth to clear minefields in the war against Iraq during the 1980s. It would be reckless for Jerusalem and Washington to dismiss the rants against the "Great Satan" and "Little Satan" as mere rhetoric. They are the rallying cries of a regime whose raison d'être is to roll back America's influence in the Middle East and usher in Israel's demise.
But let's assume Iran's nuclear quest does not necessarily serve the logic of apocalyptic politics. Let's assume Iran could be deterred from using the doomsday weapon. The question is can we afford and do we even understand the price of such deterrence? Even a rationally acting nuclear Iran may cause unacceptable harm to Western interests.
The atom bomb would enable Tehran to spread the Islamic Revolution without pushing the button. A nuclear weapon is an incredible force multiplier and -- as U.S. President Barack Obama aptly said -- constitutes a game changer. The uneasy peace that a nuclear equilibrium may guarantee tells us next to nothing about the conventional proxy wars nuclear powers tend to fight against one another.
During the Cold War, the price of the balance of terror was the recognition of spheres of influence. If Iran goes nuclear, the Western world will have to negotiate a Middle Eastern Yalta with Tehran -- one that may entail a retreat of U.S. forces from the region and an unpleasant bargain for the Gulf states and Israel. And given the geographic extent of Iran's ambitions, lines will be harder to draw than at Yalta.
Who would stop a nuclear Iran from swallowing its energy-rich neighbors or from fomenting Shia unrest in Saudi Arabia or elsewhere across the region?
Conflicts that we find difficult to resolve today will become impossible to fix, much like conflicts in Africa and Central America had to wait for the collapse of the Soviet Union in order to come to an end. While Iran may refrain from striking Israel directly, its proxies -- Hamas and Hezbollah -- will redouble their attacks and make peace between Israelis and Palestinians impossible. And a Hezbollah backed by a nuclear Iran would be able to cement its dominance in Lebanese politics, much to the detriment of the country's shrinking Christian population.
There are other dangers. "We're on the cusp of an explosion of proliferation," former U.S. National Security Advisor Brent Scowcroft recently said in a testimony to the U.S. Senate, "and Iran is now the poster child." Fearing the specter of Iranian-Shiite domination, the mostly Sunni Arab regimes will seek their own nuclear insurance. The Mideast's nuclear arms race may have already begun. The IAEA said earlier this month that it found traces of weapons-grade uranium in Egypt. The Cold War nuclear balance, though, was largely predicated on the principle of mutually assured destruction between only two powers. Can a more complex and unpredictable multipolar M.A.D. work?
Even the Soviet Union and the United States teetered on the brink of nuclear war at least once, during the Cuban missile crisis. Here were two countries that knew each other well, had diplomatic relations, and kept important official and discreet channels of communication open. And yet we came close to nuclear Armageddon.
Iran and many of its prospective nuclear adversaries do not share any of those close channels -- there is no Israeli embassy in Tehran, no Iranian embassy in Washington, no hotline between the Supreme Leader and the Saudi King. The potential for misreading, misunderstanding and miscalculating is immense, especially as Iran will pursue its revolutionary aims of changing the region in its own ideological image under the shadow of the bomb.
Yes, Iran may be deterred from launching a first nuclear strike. But we may not be able to afford the price for this achievement. That is why prevention must remain the non-negotiable policy goal of the free world.
Mr. Ottolenghi is the director of the Transatlantic Institute and the author, most recently, of "Under a Mushroom Cloud: Europe, Iran and the Bomb" (Profile Books, 2009).