I wonder why they don't agree?

Really, the headline is all you need to get the gist.
http://www.mercurynews.com/mld/mercurynews/news/politics/13639939.htm
Isn't it amazing that The United States, Britain, France and Germany already have the bomb and all think nobody else should have it, but the countries that do NOT have the bomb think they should have it?
Here is a radical idea: if you don't think OTHER countries should develop a nuclear bomb, stop researching and testing for that yourself and get rid of whatever capabilities you have in that regard already. Otherwise your hypocrisy is overwhelming and your capacity to be believed is quite underwhelming.
Do I think a nuclear capable Iran is dangerous? Yes...but I also believe a nuclear capable U.S. is dangerous, a nuclear capable Britain, France, Germany, Russia, China, Cuba, Canada, Timbuktu, or Portland, Oregon is dangerous. New flash: Nuclear bombs are inherently dangerous. They can kill and destroy, but they cannot bring life or build.
Having that capability and complaining when others want it is akin to the kid who wants to play by his rules or he is taking his ball and going home. The difference is supposed to be maturity, but instead the difference is destruction. An immature kid ends a game, an immature nuclear power ends lives. Either bring equity to the game by not complaining others want what you have or else get rid of what they want.