The people are supporting the government. You dont have to kill all the people. Just take out the nuclear facilities and blow up their refinery and let them kill each other. Many people in Iran are not aligned with their government. We could do to Iran what Iran does to other countries. Give arms and money to the factions that would destroy it like the Kurds and the college students. Iran is like a powder keg.
Keep in mind that when you help your enemy's enemy, that the new faction could be worse than the one in power. The USA has learned the hard way many times. One side can be worse than the other.
It is obvious that Iran is shipping arms and ammunitions to other groups like the Palestinians. Se we should start by blockading Iran as much as possible.
Isreal would probably bomb Iran if we let them. If we both attacked at the same time we could probably take out their defenses and their ability to attack Iraq. Of course then the world oil supply would be disrupted and we would pay for it financially. So we just cant win. Only thing left is to try to box them in or keep an eye on them and show the rest of the world their true intent.
If there were a poorer understanding of Iranian society I don't think I've ever seen it. Iran isn't like Iraq at all. There may be different opinions about the internal politics, but they aren't going to start shooting each other. It's not a cobbled together society. They were developing mathematics, art, and science when the Romans dancing half naked.
If Bush hadn't shot off his mouth like the fool he was, the moderates would most likely have eliminated the extremists. Nope, not content to let things work themselves out, he decided to call them evil and suddenly the pro-west people (and there were many) were shown to be fools and cast out.
So yeah, in another generation we might be back to where we were 8 years ago. Hopefully then we won't have a talking H-bomb as President.