This is an interesting stance, and one that should be more widely considered. My biggest worry about a nuclear-armed Iran is the potential danger when and if the Iranian regime falls to internal pressure.
I don't think that Iran would use nukes against Israel, and Romney's hard line is quickly becoming my biggest argument against his Presidency. He might just be talking the talk, but there's plenty of evidence that he goes as the wind blows. A US war with Iran would be colossally stupid, and it's a dangerous thing to beat the drums for a war that you never intend to have. War with Iran is a very serious thing, and Romney is wrong to use it as a political token.
No doubt the more that we saber rattle, the more support Iran has internally for building the thing.