Indeed, reportedly some Iranian military leaders have argued against acquiring nuclear weapons, on the grounds that they would handicap Iranian strategic flexibility and security. Among their arguments, they cite the probability that, confronted by a nuclear-armed Iran, the Gulf Arab states would be driven even further into the American orbit, and while several other adjacent countries (e.g., Turkey, Pakistan, and Russia, as an ally of the Central Asian "Stans") would probably become much less friendlier than they already are.
Seriously. They want to deter us? From what? Invading them? Stopping them from supporting terrorism? Blockading them? Do we do any of these things while Iran has no nukes? Even after Iran has sponsored terrorists to attack us?
Has Israel destroyed Iran even as Israel has nukes and Iran does not? Even when Iran sponsors terrorists who kill Israelis and Jews around the world (recall the Argentinia terror attack some years ago)?
I mean, good grief, what worse things do the mullahs want to do that they fear will finally prompt America or Israel to nuke Iran after a long history of our restraint in the face of hostile mullah actions? Now that's a scary thought.
And this doesn't even consider that Iran's fearful neighbors may go nuclear to get their own protection against Iran's nukes. Don't think they won't try. Non-Persians and non-Shias will all feel nervous about the idea of Shia and Persian Iran throwing its weight around again. Turkey will be the first but hardly the last to decide they need nukes, too.
Iran is the strongest state by far in the Gulf region. If the region (and I'll consider Israel out of the region for this purpose) remains non-nuclear, Iran will be the dominant local power. Throw in nukes and Iran's influence is blocked in theory. Press too hard and somebody else might lob a nuke at them.
Indeed, for all the complaints about our nukes, if we could guarantee that the world would remain non-nuclear with no cheaters, does anybody with half a brain think we wouldn't leap at the chance? We can't be touched in conventional combat and we'd jump for joy if we could guarantee a non-nuclear battlefield!
The Iranians are fools to want nukes. When you add that their leaders are nuts, we'd be fools to let them have nukes.
UPDATE: I may have been hasty in assuming Turkey would be the first neighbor to go nuclear in response to Tehran's success. Saudi Arabia could be hedging their bets.
Lovely decade we're having, isn't it?