Harold Myerson had a column in the Wednesday, May 30, 2007 edition of the Washington Post called "Dying for an Iraq that Isn't". The point of the column, which can be read by clicking on the link in this entry's title, is that American policy assumes that there is a non-sectarian government in Iraq which Iraqis will support. He points out that such a government simply doesn't exist. The reason why it doesn't exist is that the Iraqis themselves don't seem to want such a government. Myerson points out that in the elections in 2005 the political party that ran on a platform of a non-sectarian Iraqi government got 8% of the vote.
The presence of American troops in Iraq is not what makes Iraqis kill each other. They kill each other because they are caught up in a sectarian war pitting Sunnis against Shias, and maybe both against the Kurds. What is the role of American troops in such a situation? What side are we supposed to be helping? American lives are too precious, and too few, to waste because the American military is acting like some kind of armed referee.
Maybe Joe Biden has the best idea: create three fairly autonomous regions in Iraq and let Iraqis group together as Shia, Sunni, and Kurdish Muslims. Recognize that we can't change the culture of Iraq, only Iraqis can do that. Give the Iraqis some of that "tough love" that GOP types are always talking about.