Anyone who believes the US, UN or any other governmental body can or should prevent Iran from manufacturing nuclear weapons is misinterpreting that nation's motive.
Justifiably, we are concerned that a nation run by militant religious fanatics could use those weapons for aggression, not defense. Already Iran's president has declared his intention to destroy Israel, a politically motivated promise analogous to the late Egyptian politico Gamal Nasser's mid-century promise to "throw all the Jews into the sea."
The Arab and Persian states of the Middle East have spent the last half-century trying to do precisely that, so why would we take less seriously Iran's similar declared intention?
First, there is the matter of politics. Iran's Mahmoud Ahmadinejad, like Nasser before him, is telling his people what they want to hear. Whether the stated goal was rational or achievable has little to do with the reasons he identified it.
Consider: The US politicians of old, before radio and television made instant communication possible, would shape their message to whatever crowd they sought to impress. In states with wet and dry counties, such as Kentucky, it was not unusual for a candidate to make a prohibition speech in a dry county and an anti-prohibition speech in a wet one.
Secondly, for all his bloviating and saber rattling, Ahmadinejad knows full well that were Iran to actually attack with nuclear weapons Israel or any other nation, within an hour there would be massive retaliation from most if not all other nuclear nations.
So why bother to incur the levels of international outrage over Iran's incipient membership in the Nuclear Club? Why manufacture weapons you know you'll never dare use?
The answer has to do with prestige. Once again, turning to history, we see time and again that nations have engaged in undertakings which did them little if any actual good, but which identified them as big time players in global affairs.
The history of European colonization in Africa and Asia has been judged by historical economists, in some famous cases, as incurring net losses to the colonialists. But during the modern era, colonies were identified with visions of empire, regardless of their monetary value to the empire.
British possessions were the main example of colonies which actually paid for themselves and returned profits to the exchequer. The Dutch made smaller profits on smaller colonies, and the Spanish looted the precious metals of the New World to finance its endless wars, but on balance, these nations were the exceptions, not the rule.
The more usual case of European colonies was that of Italy, which colonized Ethiopia, especially Eritrea. The colony was a drain on the financial resources of Italians for the entire length of their stay in the Horn of Africa. But, under the Fascists especially, colonies were prestige possessions, holdings which said to the world that Italy had dreams of a recaptured Roman empire. The costs of garrisoning the colony, building public works (especially roads) and subjugating a proud and ancient people seemed worth it based not on actual return on investment, but rather upon the prestige conferred by colonial possessions.
Why do nations make such apparently irrational sacrifices? Perhaps for the same reason individuals buy bigger houses and cars than they actually need, spend more money on clothing and country club memberships than what they can truly afford, and send their children off to pricy, prestiege universities when their state schools would be not only cheaper, but often more appropriate to their kids' educational needs.
When the doctrine of "keeping up with the Joneses" goes nuclear, or subjects Third-World nations to the oppression of colonial rule, it is a sad thing.
But it is also human nature. In regard to Iran, the international community should keep the pressure on, since that nation is a well-known sponsor of state terrorism.
But worrying about a nuclear Iran daring to actually employ their nukes for anything but defense is wasted worry.
Suicide is not painless, and it is not what President Ahmadinejad seeks from his nuclear program. Noisy and demagogic he may be; nuts he is not.