Most pundits seem to be working with an understanding of the world that borders on infantile. In their worldview, leaders of nations where the people are mostly brown are always despots (e.g., Hugo Chavez), and leaders from the Middle East are always homicidal lunatics (Ahmadinejad). Thus the U.S. cannot tolerate the development of WMD by such nations - otherwise, we will be defenseless when the crazy dictator gets a wild hair up his ass and decides to take out Chicago. Are YOU willing to sit back and hope that won't happen?
Maybe there is some scenario where such a framework is appropriate; the "situation" with Iran is not one of them. Matt Yglesias, who has been surprisingly good on this issue, puts it well:
A surprisingly large number of people seem to me to be taking the view that the current president of Iran is "crazy" and therefore likely to launch an unprovoked nuclear attack on the United States or, perhaps more likely, Israel. It's worth emphasizing that under the Iranian political system the president can no more launch nuclear weapons than the Chief Justice can here in America ... it's worth understanding how incredibly unlikely this is.But people just can't seem to wrap their minds around the fact that the president of Iran is not a dictator, and does not have absolute power even within the borders of his country, even though Iran is full of Muslims. And of course, any one who harbors the slightest doubt that the Iranians are planning to attack the U.S., without provocation, is ridiculed for putting his trust in these obvious maniacs, even though they've shown absolutely no inclination towards such aggression - which is of course more than we can say for the U.S.
An unprovoked nuclear attack wouldn't be some kind of risky gamble; it would be a certain guarantee of national suicide ... Ahmadinejad, meanwhile, has spent years rising through the political system of a repressive autocracy where the leading authorities reserve the right to send you to jail and have you tortured if you piss them off. The people who rise to the top in these kind of systems are going to have to be people whose instincts for self-preservation are stronger, not weaker than your average person's. His public persona aside, if Ahmadinejad were truly someone given to flying off the rails at random times and taking actions without thinking through the consequences, where would he be today? Not president of Iran...