Critics of the Iran deal say Iran doesn’t give up much and gets a lot. It makes sense to try to get just about any deal whatsoever, though, if you assume Iran does not find it in its interests to build a bomb and is looking for a face-saving way out. (I recommend this 2009 article for an analysis of Iran’s national interests along these lines.) If you assume Iran has grand or even apocalyptic ideological ambitions, like Stalin’s USSR or Mao’s China, or that it is entirely irrational, the deal seems to make less sense. On the other hand, if Iran isn’t deterred by rational considerations like the response of other Middle Eastern nations, why should it be deterred by sanctions?
When countries view it as a kind of law of nature that their actions will lead to counteractions by other powers, their national pride doesn’t come much into play; no point in getting angry about a law of nature. So for Iran, if its acquiring the bomb leads to a Saudi bomb program or various other destabilizing and undesirable results, and doesn’t end up advancing their interests, well, no reason to do it. Diplomatically presented threats can allow communication of intentions with less guesswork, while still not ruffling feathers. But years of very public threats, and America’s denial of Iran’s perceived “right” to uranium enrichment, bring national pride into play, and the desire not to give in.
There’s counters to this argument: Iran may be rational, but doesn’t it have grand ambitions? Might they really mean this “death to America” stuff, and their rhetoric about Israel? Moreover, there’s reasons we’ve long sought to marginalize this regime as uniquely dangerous, rather than treating it as just another competitor for power: the taking of Americans as hostages, the sponsorship of terrorism, the 1994 attack on Jews in Argentina.
However, though a state functions as a single actor, it of course is the product of the actions of many people. Different people in Iran will have different ambitions. It is at least possible that we can calculate that hard-liners are out, and that a confidence-building deal will help keep them out. Indeed, the worse the deal is for the West from the perspective of critics, the better it serves as a signal of trust.