IMHO, I don't think you can draw any firm conclusion on the bomb's virtue as deterrence from the Iraqi and North Korean experiences alone. North Korea is not as economically or geopolitically important to the multinational empire as Iran, and Beijing and Seoul have said no to any adventurism on the part of Washington in the Korean Peninsula, both of which explain relative lack of Washington's action against North Korea. And if Iraq had had WMD, Washington might have still invaded it. "Israel already had a nuclear device by 1967" ("Israel Crosses the Threshold," National Security Archive Electronic Briefing Book No. 189, 28 April 2006, <http://www.gwu.edu/~nsarchiv/NSAEBB/NSAEBB189/index.htm>), but Egypt and Syria attacked the Israeli forces in the Sinai Peninsula and the Golan Heights in 1973, the Yom Kippur War. If nuclear Israel could be attacked by weak Arab armies, why can't a nuclear Iran be attacked by far more powerful armed forces of Israel and the United States?
The best deterrents that the Iranian people have on their side are economic and diplomatic ones, many of which are beyond their control: high oil prices, Moscow's and Beijing's protection, the US military bogged down in Iraq and Afghanistan, and so on. (If Arab masses could put pressures on their governments not to side with Tel Aviv and Washington against Iran and Hizballah, it would be better, but they remain weak, though they are not without influence, as the pro-Washington Arab regimes' moderation of their criticism of Hizballah, in response to domestic political opinion, showed recently.) The best military deterrents that they have are the sheer size of Iran's territory and population and its proximity to the Hormuz strait, to disrupt the oil supply through which Tehran does not need a nuclear bomb.
Since the bomb may not serve as much of deterrence, why not take the Iranian leaders at their word: they are interested in nuclear energy production? Read Muhammad Sahimi, "Forced to Fuel: Iran's Nuclear Energy Program," Energy 26.4 (Winter 2005), available at <http://hir.harvard.edu/articles/1294/>. As Sahimi argues, it looks to me that Iran's nuclear program is economically justified.
That said, Iran's development of nuclear bombs would create a new balance of terror in the Middle East, strengthening the hands of the Palestinians politically against Tel Aviv, so the pro-Palestinian faction of Iran's leadership might want to have them for this reason. -- Yoshie <http://montages.blogspot.com/> <http://mrzine.org> <http://monthlyreview.org/>