Here's an Informed Opinion on the situation in Iraq and its disastrous consequences.
Astonishingly, Sistani seems to be threatening to deploy his own militia, Ansar Sistani, if the Iraqi government doesn't do a better job of protecting Shiites and their holy sites. One lesson Sistani will have taken from the bombing of the Askariyah shrine in Samarra is that he is not very secure in Najaf, either. But all we need in Iraq is yet another powerful private sectarian militia!
Needless to say, things are looking bad in Iraq. However, people in America likely feel really bad for what is happening in Iraq. We don't want to abandon the country; a lot of people - maybe even most people - are willing to stick there and fight. Sadly, staying there will have no impact if an American presence has no legitimacy with the Iraqi people. While many would argue we already had no legitimacy, at the very least the country's Shi'ite majority were willing to work with us and its religious leaders accepted our presence and tried to remain out of the fight.
If Shi'ites are drawn into the fight, Iraq will get a lot worse. Right now, America's problems are coming mainly from a small segment of the population - the Sunni minority - which comprises less than a third of the total population. The Shi'ites are about 60% of the total population. If Shi'ite militias begin to fight Sunni insurgents or attack Sunni targets, Iraq will become totally destabilized and America will have no support in Iraq.
It is already to the point that America needs to leave. Iraq must decide it's own fate. When they do, America will owe it to Iraq to completely rebuild the mess afterwards - if Iraqis would even accept our aid. Many Americans will want to help more, but unfortunately there are consequences to actions that people often leave a sour taste. In the future, hopefully America will think twice about invading a country, especially without international support.