Because we need something to kill off the impending alien invasion
but how are we going to create the zombie hordes we are going to need?
Because Iran may become a nuclear power.
Nuclear weapons have saved the world. When was the last time there was a world war? I grew up expecting to be vaporized by an H-bomb at any moment, but it hasn't happened. One night on the 10 o'clock news they showed a video of a Russian flag over the Kremlin. All these years later, we're still alive. The threat of mutual assured destruction has proven to be a good policy after all. I know I wouldn't have wanted to be at the Somme, Vimy Ridge, etc.
because they are a deterrent to others that have them and wish us harm
Still a slight deterrence factor. But what would we do with them?
Not very easy to dispose of those.