1) The Iranian government is publicly committed to aggressive use of nuclear weapons;
2) The United States is the only power capable or willing to actively prevent this.
1) Nation-building is long, costly, and a painful drain on American civilian morale;
2) Decapitation strikes, while not cheap, are quick and have a clear distinction between success and failure.
1) Russia is a major obstacle to action against Iran, due to the profits it realizes from Iranian dealings;
2) By taking a hand in Iranian rebuilding, Russia could create a more-friendly and more profitable Iranian client.
1) Iran has shown the futility of negotiation and the desirability of negotiating (especially with the EU) in bad faith;
2) The destruction of Iran's government is the only meaningful deterrent to other, similarly inclined governments.
All of these lead to the same conclusion:
3) We should decimate the government of Iran, now
, and let the chips fall where they may.
[Hat tip: Mark Steyn
, via Tim Blair.]