Political scientist Kenneth Waltz wrote a piece in Foreign Affairs entitled Why Iran Should Get The Bomb (beware: it’s behind a paywall), which obviously drew a lot of attention. He was then interviewed by an Asian-Pacific magazine called The Diplomat, with whom he discussed the position that proliferation of nuclear weapons is actually a great idea. His main point: World War III never came. Since the end of the second world war in 1945 with the only wartime detonations of atomic bombs in history, the major world powers have enjoyed the unprecedented state of peace now known as Pax Americana:
On one hand the world has known war since time immemorial, right through August 1945. Since then, there have been no wars among the major states of the world. War has been relegated to peripheral states (and, of course, wars within them). Nuclear weapons are the only peacekeeping weapons that the world has ever known. It would be strange for me to advocate for their abolition, as they have made wars all but impossible. — Kenneth Waltz
He goes on to point out that the nuclear deterrent is so strong that even the most bitter of rivals — Soviet Russia and the US, Soviet Russia and China, Pakistan and India — have not risked going to war with each other and bringing about mutually assured destruction. Two countries that possess nuclear arsenals are forced to find peaceful solutions to their problems; and the inevitable skirmishes that happen are quickly resolved, lest they escalate into nuclear war. It’s hard to imagine World War II having happened if Poland and France had nuclear weapons.
In this light, the main problem with states like Iran gaining nuclear weapons is not the risk of nuclear war, but the fact that it puts them on a more equal footing: we can’t invade Pakistan the way we did Afghanistan and Iraq, which makes nuclear states harder to bend to our will. (There is also the risk of something going wrong — computer malfunction, sabotage, theft — which could lead to a nuclear explosion, but presumably if a state is sophisticated enough to develop nuclear weapons, it’s sophisticated enough to secure them, too.)
Right now, Israel presumably has the bomb, is the only nation in the Middle East that does, and its military hegemony over the region is causing instability. If Iran were to also have nukes, the effect would ironically be to stabilize the the Middle East because neither state could act against the other — they would be at a stalemate. In contrast to Israel’s interests, that balance of power and the resulting stability is exactly what America wants: peace would keep the price of oil low, diffuse terrorist tendencies which arise from the hopelessness of ever winning a conventional war, and remove the need for American military involvement in the Middle East.
Of course, for this scenario to work without plunging the world into nuclear winter, it would require that all nuclear weapons be in the hands of sane people. Given the recent rulers of Iran and North Korea, that may not be a wise assumption.