I don’t have much to add to this:

[C]onsider why the United States, China, and Russia–or any other country for that matter–should fear nuclear proliferation. Of course, there are the concerns of accidental nuclear detonation, nuclear terrorism, or even nuclear war. But these are all extremely low probability events. The primary threat of nuclear proliferation is that it constrains the freedom of powerful states to use or threaten to use force abroad. […]

Some analysts argue that we shouldn’t worry about proliferation in Iran because nuclear deterrence will work, much like it worked during the Cold War. But from Washington’s point of view, this is precisely the problem; it is more often than not the United States that will be deterred. Although Washington might not have immediate plans to use force in the Middle East, it would like to keep the option open.

Of course, as time goes to infinity even “low probability events” become inevitable. So there is also that.  But even leaving that aside, the smart move for the US – for the world – in trying to stop proliferation would be to try to make nuclear weapons less important in international relations.  Reduce our own stockpiles, for example.  Maybe allow Brazil, or some other non-nuclear country, a place on the UN Security Council.  Stop bombing fools so they don’t feel such a strong need to deter you.  Stuff like that, but especially the first one.  Because while I don’t like the idea of North Korea and now Iran having a few rudimentary A-bombs, I’m not sure I like the idea of Ayatollah Starbursts getting her grubby mitts on a few thousand megatons of nukes, and the ability to deliver them anywhere on Earth in 30 minutes, any better.  You betcha.