The problem with nuclear weapons in the 21st century is not the nuke-a-city and mass destruction via fallout type that we worried about in the containment era.
The problem is a small tactical nuke combined with modern day rocketry available to states such as Iran, S. Korea, and any South American country poses a threat in the form of an EMP. Any small nuke detonated in the atmosphere above the earth will completely fry the entire electrical grid and all electronic devices on the earth's surface in a wide range.
This is also why the Iranian bomb is in fact a threat. As is the N. Korean bomb. Our leaders do a totally totally ty job of explaining the threats to the people, instead relying on republican jingoistic babble 101.
It's bad enough N. Korea has the ballistic missle capabilities of reaching LA, if they kept advancing, and a small nuke was exploded in the atmosphere above LA, a huge chunk of the country's westside electrical grid would be totally shut down, and thousands if not millions would die. It's not as simple as just turning the juice back on.
Problem is people think it's just a problem of part of a city getting nuked....that's not the true nature of the threat in the 21st century. Containment in that aspect is still fully functional.
Manny touched on this but I think its an even bigger loss of power than most would think if we allowed a state in our own hemisphere to become a nuclear power.
It would be a huge huge deal from a security standpoint if we allowed this to happen.