Why wait to disarm Iran?
Iran is as much a pistachio-and-rug-exporting country as it was when the sadistic medievalists first seized power. So it wouldn't be surprising in the least if a regime that has no genuine respect for science and no internal self-critical feedback had screwed up its rogue acquisition of modern weaponry. A system in which nothing really works except the military and the police will, like North Korea, end up producing somewhat spastic missiles and low-yield nukes, as well.
If there's no saber in the scabbard, then at least don't make the vulgar mistake of rattling it. Against this, we are at least entitled to consider the idea that a decaying regime that is bluffing and buying (or rather stealing) time on weapons of mass destruction is in a condition that makes this the best moment to do at least something to raise the cost of the lawlessness and to slow down and sabotage the preparations. Or might it be better to wait and to fight later on more equal terms? Just asking.
Maybe, just maybe, Iran has moved back from the brink. It now appear to be with us in fighting the Islamic State, but let's not forget that the Iraqi Shi'a sectarian regime was backed by Iran.
Iran may have moved one step away from the brink, but it still sponsors Hamas, Hezbollah and so intervenes egregiously in Iraq, Syria and Palestine. It still maintains a system that glorifies death and enslaves the population to Islamism.
Iran's case for having nuclear weapons for defensive purposes can only be if it considers itself at risk from neighbours, and Iraq under the Islamic State would be the most obvious risk. If the West and Iran together work on nullifying that threat in Iraq, could there be a path for Iran to open up its nuclear facilities? Or is Iran actually remaining on the path of having an option to take on Israel?