In the region, Persian Iran will immediately become the hegemonic power in the Arab Middle East. Today it is deterred from overt aggression against its neighbors by the threat of conventional retaliation. Against a nuclear Iran, such deterrence becomes far less credible. As its weak, non-nuclear Persian Gulf neighbors accommodate to it, jihadist Iran will gain control of the most strategic region on the globe.To be fair to CK, he does at least give a scary list of the likely consequences of such an attack.
Then there is the larger danger of permitting nuclear weapons to be acquired by religious fanatics seized with an eschatological belief in the imminent apocalypse and in their own divine duty to hasten the End of Days.
The mullahs are infinitely more likely to use these weapons than anyone in the history of the nuclear age. Every city in the civilized world will live under the specter of instant annihilation delivered either by missile or by terrorist. This from a country that has an official Death to America Day and has declared since Ayatollah Khomeini's ascension that Israel must be wiped off the map.
Against millenarian fanaticism glorying in a cult of death, deterrence is a mere wish. Is the West prepared to wager its cities with their millions of inhabitants on that feeble gamble?
CK doesn't seriously consider any of the alternatives, the possibility that his assessment of Iran is dead wrong, the preparation and mobilization necessary if a serious attack on Iran were to be launched, the moral questions involved in another probably unsuccessful bombing campaign, or the significance of the presence in this country of an Iranian diaspora.