Israel should not attack Iran. Nor should it solicit American action to that end. Based on historical precedents, if Israel had a surgical way to thwart Iran's nuclear ambitions, it would have done so already. Hence, on the assumption that such an elegant solution is not available, the cost of an Israeli strike does not seem commensurate with the reward. Further, the potential cost, and likelihood, of living with a nuclear Iran does not seem high enough to justify a wager of this kind.
Let's look at the best case scenario of an Israeli attack: Following a successful strike, Israel remains the region's sole nuclear power. The ensuing response from Iran's proxies provides the Israeli government with political capital to act against the hoards of short and medium range missiles in Lebanon and Gaza (and possibly Syria), leaving the country's enemies diminished. The morning after the war Israel will still be surrounded by failed states and restive populations on track to become proxies of the region's next "rogue state"; Israel would still be isolated, insecure, and its right to exist would still be questioned (probably for illegitimate reasons, but questioned nonetheless); Israel would still be a thriving liberal democracy surrounded by despots that rely on the vilification of the Jewish state to retain their power. Such despots - in Syria, Saudi Arabia, Egypt, New Libya, or even a post-war Iran - may choose to develop or acquire nuclear weapons at any given moment. They may do so faster and more clandestinely than Iran. To use two recent examples, Libya was on the verge of developing nuclear weapons until it voluntarily gave up its program, and Syria was not far behind and was set back only thanks to a singular intelligence effort.
Let us consider a less ideal scenario: Imagine a world containing a large muslim country armed with nuclear weapons; a country that does not formally recognize Israel's right to exist; a country that supports Israel's enemies and provides training grounds and equipment for insurgents bound for Lebanon and Gaza; a country that harbors terrorists and undermines US and Israeli interests; a country that does not share a border with Israel, but is close enough to launch missiles.
In fact, the previous paragraph describes a country that already exists - Pakistan. Pakistan became a nuclear power during the previous decade. This did not make the world a better place, but it was not the end of the world either. True, Iran is not Pakistan. The latter's ambitions are tempered by strong neighbors (India, and to a lesser extent, China) and the former's rhetoric and support of attacks on Israeli civilians have been more pronounced; Iran is, at least putatively, guided by religious clerics while Pakistan, also putatively, is a secular state controlled by generals. All that does not detract from the comparison. The world is not likely to end the day Iran acquires nuclear weapons.
Pakistan and Iran have another thing in common: Both developed their nuclear programs while America was busy invading their neighbors; both benefited directly by freeing resources that were previously dedicated to tensions along their borders, and indirectly by staying out of the limelight while the international community was busy elsewhere. Pakistan also benefitted from its status as a US ally vis-a-vis Afghanistan, while Iran gained precious time by letting on that it might one day become such an ally vis-a-vis Iraq.
Nonetheless, the risk of Iran obtaining nuclear weapons is severe. It would change the global balance of power, but it is important to acknowledge that the balance has already changed. Nuclear weapons, like luxury goods, were once produced only by the world's leading countries (even the USSR was at the height of its power when it developed them). Back then, being a nuclear power meant being a member of a small and prestigious circle, admission to which was contingent on an approval - by commission or omission - from existing members. In the current age of free-flowing information and capital, nuclear warheads are not the trump card they once were. They no longer guarantee geopolitical status. In a multipolar world - and potentially at the hands of non-state actors - a notion of global stability under a nuclear cloud of Mutually Assured Destruction is no longer valid. Whether we like it or not, the only thing nuclear weapons contribute to is the likelihood of death and destruction.
Thus, it is in the interest of the world - including established and nascent superpowers - to pursue nuclear disarmament across the board. American (or Chinese, or Israeli) military power is awesome enough without nuclear weapons and is enough of a threat against a sovereign aggressor. Against non-state entities, the threat of nuclear retaliation is anyhow irrelevant. The world should be free of nuclear weapons altogether. We are not great fans of the United Nations, but if that organization should exist, it has no greater mission. Ironically, the fact that the UN is now largely controlled by the world's rogues and disenfranchised can facilitate resolutions to that end. The fact that China's nuclear arsenal is far smaller than America's might encourage the former to support such an initiative. Following the surprise attacks of September 2011 and the US Army's growing engagement with non-state actors, the American public might also warm up to the vision of a nuclear-free world. The other nuclear powers will follow a Chinese and American lead.
It would be a great challenge to clear the world of nuclear weapons, but it is not beyond imagination. It would cost less, do more good, and garner more public support than the current crusade against fossil fuels. Israel and the US, two of the world's leading proprietors of renewable energy technologies (and of natural gas), could lead the initiative. China, the world's most dependent energy consumer, could also play a leading role. With the Middle East on the brink of a nuclear arms race, a major war, or both - timing has never been better.