Because if the attack fails, the Middle East will almost certainly face a nuclear war — either through a subsequent pre-emptive Israeli nuclear strike or a nuclear exchange shortly after Iran gets the bomb.
He admits that if Israel's conventional strike fails, there will be Iranian counterattacks, both directly and through Iranian proxies like Hizbollah and Syria. He also says that it's unlikely that Western countries will then force Iran to abandon its nuclear program, which Iran will in turn work on even more strongly. His argument then slides into the possibility/probability that Israel will launch a nuclear first strike against Iran before Iran succeeds in building a nuclear weapon.
Such a situation would confront Israeli leaders with two agonizing, dismal choices. One is to allow the Iranians to acquire the bomb and hope for the best — meaning a nuclear standoff, with the prospect of mutual assured destruction preventing the Iranians from actually using the weapon. The other would be to use the Iranian counterstrikes as an excuse to escalate and use the only means available that will actually destroy the Iranian nuclear project: Israel’s own nuclear arsenal.
Given the fundamentalist, self-sacrificial mindset of the mullahs who run Iran, Israel knows that deterrence may not work as well as it did with the comparatively rational men who ran the Kremlin and White House during the cold war. They are likely to use any bomb they build, both because of ideology and because of fear of Israeli nuclear pre-emption. Thus an Israeli nuclear strike to prevent the Iranians from taking the final steps toward getting the bomb is probable. The alternative is letting Tehran have its bomb. In either case, a Middle Eastern nuclear holocaust would be in the cards.
Morris should not have written this article and the New York Times should not have published it. I think that this is one of the most irresponsible articles I have ever read. I think that it is quite possible to read Morris' article not only as descriptive of what might happen, but also as urging Israel to attack Iran conventionally, and if that doesn't work, launch a nuclear war against it. The Israeli government doesn't even admit publicly that it has a nuclear capability.
I assume that Morris really cares about Israel - if so, why is he writing such inflammatory words in an already dangerous situation? Not to speak of the moral implications of such a possibility - hasn't Morris thought about the absolute immorality of launching a nuclear first strike on a nation which has not attacked Israel?
Physicians for Social Responsibility produced a report in 2006 on the consequences of an American nuclear strike on Iran (using nuclear bunker-buster bombs with the purpose of destroying its underground nuclear installations in addition to conventional bombing). They estimate that about 2.6 million people would die in the first 48 hours after the attack. In the wider region, over 10 million would be exposed to significant radiation. (See the article for complete information and how they arrived at the numbers).
We should not be listening to Benny Morris and I hope that someone high-up in the Bush administration is informing the Israeli government right now that such an attack should not even be contemplated.