When Pakistan finished its nuclear weapons they were being ruled by fanatical islamists friendly to the taliban and dedicated to war with India. General Musharef and several supporters in the officer corps said "WHOA hold on there you nut-jobs. In a Nuclear war everyone looses and nobody wins." and they bumped the fanatics out of power.
Once you have nuclear weapons you can't screw around any more, you can't make random threats and invade other countries. Iran could never even hope to loose well in a nuclear war. Our second strike capability is massive. A single trident submarine has an arsenal capable of killing everyone on earth two and a half times. Pretty sure they are the tridents. And we have around twenty of these things. They will never be able to fight us then because if they strike first we kill them all, and if they don't strike first we kill them all to keep them from striking first. The only way Iran gets out of that situation alive is if you make damn sure no one thinks they are about to strike first, or even thinking about it.
Strategically it is the worse thing they could ever do to develop nuclear weapons. Their own people will turn on them to save themselves. We have the ability to make sure they have no launch capability left because every square inch of the country can be reduced to slag. And don't think we wouldn't do it. Countering with a first strike would be the onlyoption and you have to use nukes becuase you have to be sure and its the only way to be sure. There is no place that can be made safe from a precision guided nuclear warhead. The US is the only country to have ever used nuclear weapons in war, and all other countries know it.
Iran would be fools to develop weapons that would make us resort to such a thing. Or more likely that would make them have to shut up while we stomp around making the world safe for democracy. They wouldn't dare ever even threaton to put forces in the field against us. Kim Jong Il has discovered that the only thing you can do with nuclear weapons is sell them. The US doesn't cower back in fear.
But if you thought Oil prices are high now, that would be a mess.