I think many people don't seem to realise that one of the biggest dangers of the Iranian leadership developing nuclear weaponry is not that it will use them on Israel or the USA, but that it will start supplying terrorist groups who can operate without the fear of retribution that would occur if a nation were to attack using nukes. Nuclear technology does not have to be very advanced to create a highly dangerous bomb. It doesn't even have to work properly - it would be enough to spread lumps of radioactive material across an area making it uninhabitable. To whom might the Iranian leadership donate such a device and where might it be used? Maybe a Palestinian militant group or Al-Qaeda against Israel? Probably. Maybe attempting to shut down and permanently contaminate a large chunk of Saudi Arabia's oil production? Potentially. What about some Kashmiri separatist faction? Quite possibly. Chechnya? Perhaps. Those who think that the only likely targets are Israel, the US and the UK should think again before allowing a very dangerous group of individuals to get their paws on knowledge which, once obtained, can't be undone.
There is evidence that Iran is currently supplying terrorist groups in Iraq, simply to keep the West bogged down and distract attention from themselves. I don't think that they can be trusted yet with some of the most dangerous technology we know about.