The whole point of this thread is you pitching a fit and withdrawing your support from the war because you, in your infinite wisdom, think the Mahdi Army should be taken down by US forces, now, before they ethnic cleanse the Sunnis and wipe out the Badr Brigades.
It's simply not as easy as one thinks..... I don't care what the pundits say, Al-Sadr has popular support, when he barracated himself in that holy Shitte mosque- Where was the outrage? From his fellow Iraqs? There was none!
I often disagree with jmc, especially on Sunni/Shia relations, but he's entirely right on this point. While I find the thought of the Iraqi Sunnis driven to ruin both comforting and cathartic, it is certainly not in our interest to allow the Madhi Army to do so.
Letting al-Sadr take over Iraq entirely, in order to set up a theocratic satellite state of Iran, with AQI as the leader of the Sunni resistance, and America forced to withdraw under fire, is a merger of worst case scenarios. We'd have been a lot better off leaving Saddam in power if this is how it's going to end.
What benefit would the U.S. derive from, as you say, allowing the Madhi Army to ethnically cleanse the Sunnis and wipe out the Badr brigades?