Bill Keller, columnist and former executive editor for the New York Times, writes: [T]here are serious, thoughtful people who are willing to contemplate a nuclear Iran, kept in check by the time-tested assurance of retaliatory destruction. If the U.S. arsenal deterred the Soviet Union for decades of cold war and now keeps North Korea’s nukes in their silos, if India and Pakistan have kept each other in a nuclear stalemate, why would Iran not be similarly deterred by the certainty that using nuclear weapons would bring a hellish reprisal?

Anyone who has a glib answer to this problem isn’t taking the subject seriously. Personally, I’ve tended to duck it, taking refuge in the hope that the tightening vise of international pressure — and a few cyberattacks — would make Iran relent and spare us the hard choice. But that could be wishful thinking. So I’ve spent some time reading and questioning, trying to report my way to an opinion.

Let’s assume, for starters, that Iran’s theocrats are determined to acquire nuclear weapons. Western analysts say there is no evidence yet that the supreme leader has made that decision. But if you ruled a country surrounded by unfriendly neighbors — Persians among the Arabs, Shiites among the Sunnis — a country with a grand sense of self-esteem, a tendency to paranoia and five nuclear powers nearby, wouldn’t you want the security of your own nuclear arsenal?

Let’s assume further that diplomacy, sanctions and computer viruses may not dissuade the regime from its nuclear ambitions. So far, these measures seem to have slowed the nuclear program and bought some time, but Iran’s stockpiles of enriched fuel have grown in size and concentration despite everything a disapproving world has thrown at them so far. So, then what?

A pre-emptive bombing campaign against Iran’s uranium factories would almost certainly require major U.S. participation to be effective, and would not be neat. Beyond the immediate casualties, it would carry grave costs: outraged Iranians rallying behind this regime that is now deservedly unpopular; Iran or its surrogates lashing out against American and Israeli targets in a long-term, low-intensity campaign of retaliation; a scorching hatred of America on the newly empowered Arab street, generating new recruits for Al Qaeda and its ilk; an untimely oil shock to a fragile world economy; an unraveling of the united front Obama has assembled to isolate Iran. All that, and a redoubled determination by Iran’s leaders to do the one thing that would prevent a future attack: rebuild the nuclear assembly line, only this time faster and deeper underground. There is a pretty broad consensus that, short of a full-scale invasion and occupation of Iran, a preventive attack would not end the nuclear program, only postpone it for a few years.

Now imagine that Iran succeeds in making its way into the nuclear club.

Despite the incendiary rhetoric, it is hard to believe the aim of an Iranian nuclear program is the extermination of Israel. The regime in Iran is brutal, mendacious and meddlesome, and given to spraying gobbets of Hitleresque bile at the Jewish state. But Israel is a nuclear power, backed by a bigger nuclear power. Before an Iranian mushroom cloud had bloomed to its full height over Tel Aviv, a flock of reciprocal nukes would be on the way to incinerate Iran. Iran may encourage fanatic chumps to carry out suicide missions, but there is not the slightest reason to believe the mullahs themselves are suicidal.

The more common arguments against tolerating a nuclear Iran are these:

First, that possession of a nuclear shield would embolden Iran to step up its interference in the region, either directly or through surrogates like Hezbollah. This is probably true. But as James Dobbins, a former diplomat who heads security studies for the RAND Corporation, told me, the subversive menace of a nuclear Iran has to be weighed against the lethal rage of an Iran that had been the victim of an unprovoked attack.

A second worry is that a Persian Bomb would set off a regional nuclear arms race. This is probably an exaggerated fear. A nuclear program is not cheap or easy. In other parts of the world, the proliferation virus has not been as contagious as you might have feared. So the Saudis, who regard Iran as a viper state, might be tempted buy a bomb from Pakistan, which is not a pleasant thought. But Egypt (broke), Turkey (a NATO member) and the others have strong reasons not to join the race.

Most worrisome, I think, is the danger that a crisis between Israel and Iran would escalate out of control. Given the history of mistrust and the absence of communication, some war planner on one side or the other might guess that a nuclear attack was imminent, and decide to go first.

“You would have a very unstable deterrent environment between Israel and Iran, simply because these are two states that tend to view each other in existential terms,” said Ray Takeyh, an Iranian-American Middle East scholar at the Council on Foreign Relations, who is not an advocate of containment. Against this fear, history suggests that nuclear weapons make even aggressive countries more cautious. Before their first nuclear tests, India and Pakistan fought three serious conventional wars. Since getting their nukes they have bristled at each other across a long, heavily armed border, but no dispute has risen to an outright war.

At the end of this theoretical exercise, we have two awful choices with unpredictable consequences. After immersing myself in the expert thinking on both sides, I think that, forced to choose, I would swallow hard and take the risks of a nuclear Iran over the gamble of a pre-emptive war.