It's a ghastly arighmetic, but it ought to be done: a nuclear strike against Iran would kill many, but it can decisively bring the country to its knees and nip in the bud a coming clash of civilizations that would in the long run result in far more deaths and suffering.
This would work best if it's part of an operation against Iran's larger and even more dangerous ally, Russia. Don't forget that the US has come to be in a position where it can execute a pre-emptive counterforce nuclear strike against Russia: http://belfercenter.hks.harvar...
The silo locations are known and the mobile katyusha launchers are being tracked. That only leaves submarine launches as a retaliatory possibility for the russkies, which would be sufficiently few to be mopped up by missile defense. Given the Russian populace's fervent nationalism, their deep-seated need
to be ruled by tyrants -- from the tzars through the commies to Putin, and their propensity to export their brotherly love to their unfortunate neighbors, justification for neutering the evil now is easy to come by.
Any fellow Canadians reading my post: lest you disagree, I remind you the Russian bear has its eye on the whole arctic, and the current framework under which negotiations over territory are unfolding is but a game: a signature to any resultant agreement will be no more binding to the Russians than their signature was on the Budapest Memorandum of 1995 which gave Ukraine security assurances in exchange for them giving up their nuclear arsenal. The Russian doesn't understand diplomacy, agreements, international law, or honor -- he only understands force, and perceives the lack of aggression as weakness.