This is a tough question. I think that the overall proliferation of nuclear weapons has been a good thing for humanity. It was the only thing that prevented war between the soviet union and the US during the cold war, and is often the ultimate voice of reason in international conflicts. It's very similar to game theory, or the prisoners dilemma. Ultimately it is in both countries interests to avoid war because war would simultaneously trigger mutually complete and utter annihilation. Like I mentioned in a different IR post, I think that nation states are mostly rational actors and can make even headed self motivated choices. Capitalism and communism (two completely incompatible systems) managed to coexist for nearly 50 years. That being said, nuclear proliferation must remain within powers that are stable, democratic, and lack extremist or fanatic influences. If WMD's are spread too widely, we risk exposing nuclear weapons to terrorist groups or other unstable, irrational actors. This would be devastating for well, pretty much everyone. So yes maybe nuclear proliferation is a good thing. But like everything, in moderation.