A world without nuclear weapons is a better place, but a nuclear Iran would have some advantages we should be aware of. In measuring the cost efficiency of a war against Iran, one must take into account that nuclear weapons in Iran's hands would result in a balance of terror in the Middle East, which may benefit the region in some way.
This balance of terror creates an effect that decreases the probability of war. As the expected extent of damage to the countries participating in any war increases, the sides become more cautious. British philosopher Bertrand Russell famously referred to the Cold War as a game of "chicken" between two teenagers driving toward each other on a collision course. One of the drivers must swerve, or both may die in the crash, but if one driver swerves and the other doesn't, the one who swerved will be called a "chicken," meaning a coward. Russell used the analogy to support his call for nuclear disarmament – as the possibility of a "crash" exists.
In this game, as the expected extent of the damage from the crash increases, the probability of a crash decreases. So, if a "crash" would result in a nuclear holocaust, the probability that it will actually occur is smaller.
The main points of this theory were proven true in the conflict between India and Pakistan: Both countries fought a number of wars since their inception. After developing nuclear weapons, the conflict between them reached a level of intensity which in the past would have led to a major war, but not this time. This time, they were more cautious. It appears that this balance of terror was one of the reasons the Cold War did not escalate into a full-scale armed conflict.
Moreover, nuclear arms in the hands of multiple countries motivates the rest of the world's nations to do all they can to prevent an armed conflict. They realize that such a war may end in a nuclear holocaust. Therefore, in the event that Iran develops nuclear weapons, we should expect greater global intervention in the Mideast conflict. This intervention would ultimately increase the probability of resolving the dispute.
In addition, a nuclear Iran may help defuse tensions surrounding the Israeli-Palestinian conflict. For example, it may encourage Israeli society to abandon symbols such as the Temple Mount and Greater Israel, and perhaps lead Israel to end the occupation or agree to regional demilitarization.
Of course, a nuclear Iran would also have significant drawbacks. A world without nuclear weapons is a better place, so I believe countries should strive for bilateral disarmament agreements. But when considering the risks involved in an Israeli attack on Iran, the significant advantages of a nuclear Iran become even more apparent.
Uri Weiss teaches university level Game Theory and Legal Negotiation