The problem about develop wide destruction weapons is sometime your enemy will have the same weapons as you.
As USA is the only major nation in the world (speaking about army/weapons), what about USA propose that everybody destroy all nuke weapons (USA including) and revert again to regular war?
Although building an atomic bond is "easy", those guys cant make one without the proper tecnology, that inst avaliable on store next door. They can get one :
1) stealing components
2) stealing a complete bomb
3) buying a complete bomb
Options 2 and 3 are worldwide available (Russia, China, Israel, Pasquitan, India)
If nobody produce bomb and/or components, no one will have one. easy, isnt it?
But USA, despite having a huge arsenal of "regular weapons", still wants to keep its nuclear weapons.
Lets offer other example: instead thinking about Al-qaeda, what about the USA terrorist (home made ones)?
I think they have more chances to get one (maybe from USA arsenal) than those crazy Al-qaeda guys.

Please dont compare 9/11(a tragedy) with Hiroshima/Nagazaki bombing. Its not the same subject and are uncomparable.