I seriously disagree with bombing Iran if diplomacy fails but I also disagree with your way of thinking..
Do I think that Iran would sit there and take it? Uhm... yeah.. pretty much.. I don't think they will unleash hell on us, I think they will sit In Iran and watch their precious army be blown to bits by a superior war machine.. In the first gulfwar Sadam had shitloads of tanks but they couldn't even dent the US forces, Iran would be no different.
America might not be capable of peacefully occupying countries to enforce democracy but it is perfectly capable of blowing inferior armies to bits.
Which once again, is not to say that you should.. It would be terrible if it happened and the US doesn't have the means to stably occupy a country with four times the population of Iraq. But blow them to bits? Yeah.. you could, and you would probably not even loose a single carrier in the process of doing so.