Remind Me Again Which Side We're On

I've never heard a good explanation as to why the United States is fighting for the Shiite majority against the Sunni insurgency in Iraq rather than the other way around. Would anyone really mind or even notice if tomorrow we just switched sides? I personally don't care whether Shiites or Sunnis rule Iraq. I can never even remember what the difference is between them, and I've taken a few world religion classes in my day. Which side claims to be the successors of Mohammed's brother-in-law again? I can't remember, but why should I care? Much less sacrifice the future of my country on behalf of this inane conflict? Just divide the bloody thing in half, declare victory, and come home, no? I have these thoughts every time I hear the politicians and analysts talking about how progress in Iraq is measured in terms of Iraqi security, i.e., our efforts to train and equip the Shiite majority to effectively fight the insurgency on its own. There is no good reason I can think of for us to want to do this. Getting involved in other countries' civil wars is never a good idea. What we should be doing is negotiating a cease fire and a peace agreement between the two sides. What we need to be is an honest broker in the region, a force for peace and justice rather than division and conflict. If we could actually settle the conflict between the Sunnis and the Shiites and bring peace to Iraq, that act alone would probably do more than anything towards repairing our damaged reputation and our long term goals vis a vis the Muslim world.