Deterrence

Hopefully, Iran doesn't have any historians -- or people with IQs above, say, 80. 'Cause if it does, as Dilip Hiro points out, then the Iranian leadership will come to the realization that they have every reason to get a nuclear weapon.

As should be obvious by now, the US could care less about nuclear proliferation. It simply doesn't want strategic adversaries to have nukes, largely for their deterrent potential. Having a nuke sitting on the platform makes it vastly more difficult to attack countries and conduct "regime change."

The indifference to nuclear proliferation, generally speaking, was made crystal clear when Washington announced it would be handing the nuclear keys over to India last year, in violation of its own obligations under the NPT. Amazingly, this was done precisely while the Iranian issue was being bandied about by the IAEA, but hardly any commentators in the US were impolite enough to note the hypocrisy.