The number of nations maintaining a nuclear arsenal should be going down, not up. Instead of Iran obtaining nuclear weapons, those nations maintaining an arsenal should be dismantling theirs. Only a total ban on nukes is right and proper. Of course, since the United States continues to block bans on landmines and cluster bombs, I wouldn't hold my breath.
Beyond that, I don't think there is any serious doubt that the Iranian regime is attempting to obtain nuclear weapons. The United States has been consistently threatening Iran since 2002, maintains a ring of military bases completely surrounding Iran as well as a naval presence in the Persian Gulf, and in the past decade has conducted two large-scale ground invasions of nations bordering Iran, one on either side. I think it would be very difficult for an objective observer to argue that the United States does not pose a grave military threat to Iran's security. It is a natural step for the regime to attempt to obtain the most devastating weaponry possible in self-defense. That said, I really don't think they'll ever get there. The current US President has attacked more countries than his predecessor, and the endless global conflict has continued to escalate as it did in the previous decade. I think the United States, or more likely its client Israel, will strike first. (Israel has also made more or less constant threats against Iran, and conducted a land invasion of its own in 2006.) With the unmanned aerial drone that was taken down over Iran last month, the United States is already undeniably conducting covert military operations in Iran.