Casualties under Saddam were estimated to be 300k to 500k. A third to a half of what "shock and awe" has cost, twice as many in roughly half the time, and ongoing.
The hard decision is to do nothing. Yes, let them stew in their own juice. Freedom fought for is freedom hard earned. Nobody seems to know what to do with freedom when it is handed to them on a plate. As I said in an earlier post, the end game after the invasion should have been to cut Iraq into three parts along old tribal boundaries - but that would be unpopular with everyone too, as it would strengthen the call for an independent Kurdistan taking in bits of Iran, Turkey and Syria .... but it's too late for that now.
Getting rid of Assad would only compound the situation. And don't even think of trying to oust the Iranian leadership. The topography is extremely hostile to invading forces and they have a battle-hardened infantry used to the landscape.
