The "logic" being that a rogue state would only use them as a deterrent, and that a terrorist group can create mass panic in easier, more creative ways. The largest problem with this logic, is that these two groups themselves aren't really known for acting logically.
So a nuke-free world -- as desirable as it would be, for strategic reasons, from an American perspective -- is probably not in the cards, as long as some weak and worried countries think that nukes enable them to deter attack by other nations on the cheap. That being the case, how alarmed should we be by the possibility that states or stateless terrorists will use nuclear weapons?
If these rogue states are able to begin manufacturing nuclear weapons "on the cheap", we should be pretty alarmed I'd say.
Since the 1970s, I have been reading nonproliferation experts who write solemnly that in the next decade there is a 20 percent or 50 percent or 100 percent chance that an atomic bomb will go off in a major city. Decade after decade, they tell us that a city will be incinerated within a decade, and it never happens.
Yes, we haven't yet had a city incinerated. But we didn't have a country quite like North Korea manufacturing nuclear weapons in the 1970s.
A conventional superpower like the U.S. should consider unilaterally renouncing the use of mass-casualty nuclear weapons not only in first strikes but also in retaliation.
I think I see a flaw here. If we announce that we will never use our nuclear weapons, even in retaliation, they sort of stop being a deterrent. And our conventional forces won't be a strong enough deterrent against countries with a large nuclear stockpile.
Iran would be much more alarming if instead of trying to obtain nuclear weapons it were building up a first-rate navy, a long-distance air force and an enormous army capable of occupying one or more of its neighbors. The fact that it is not doing so suggests that the nuclear weapons capability it evidently seeks is for deterrence, not offense.
Ok, lets give Iran and North Korea the benefit of the doubt and say they are only seeking nuclear weapons as a deterrent. That's still a very bad thing. Sure they don't have much of a navy, but in the case of North Korea, they have a pretty big army, and making themselves invasion-proof via nuclear weapons may give them the ego to throw it around.
Not only that, but what happens if the country falls apart? What happens if there's a military coup? What happens if some of these nuclear weapons disappear into the black market in the confusion? Neither country is what I'd call stable. Then if a terror cell happened upon a pre-owned discount atom bomb at Black-Market-Weapons-R-Us, I somehow doubt they'd pass up on it.
The bottom line is, do I think we should live in constant fear, afraid that we may be atomized at any moment? No. Should we be worried about North Korea and Iran? I'd give that a definite yes.