Since America can't afford to play the games with Iran that they have played in Iraq, and as an alternative to what H. Clinton said, why doesn't America simply say to the Iranian public: "Your government has ___ days to destroy the nuclear plants OR for you to overthrow the gov't, otherwise WE will destroy the nuclear plants ourselves--and if ANY threats of counter attacks are carried out, which we simply cannot handle, then we will destroy Iran." This may also be the best way for the Iranian public to spare their own lives by circumventing other possible developments. You don't think the Iranian people can & would cooperate? I leave this thread to others to take over.
There is one important issue you have not factored into the equation. In theory, you are correct but the assumption is that you are dealing with rational people and a great deal of those that come from that part of the world are the furthest thing from rational you will ever find. Threatening muslims with death is no different than threatening to shoot a suicide bomber with a packed vest of explosives. You are applying the mutual destruction argument that worked so well in the cold war with the soviets to people who don't respect life and glory in death.