Via QandO, I see that Charles Krauthammer has a "clever" response for those (like me) worried about the Sunnis boycotting the January election:

In 1864, 11 of the 36 states did not participate in the presidential election. Was Lincoln's election therefore illegitimate?

But "legitimacy" isn't the main concern here! Violence and destruction and mayhem are. The trouble with leaving the Sunnis out isn't that it will offend some democratic ideals; it's that those marginalized Sunnis happen to have access to a very well-organized and lethal insurgency—one that, with enough manpower, would be stronger than anything a newly elected Iraqi government would have. The goal of the entire political process is to stop the violence in Iraq by drawing a good portion of those Sunnis in. Failing that, I don't see what the point is. Maybe to let the Shia develop a new strand of democratic Islamic politics. But that will be awfully hard to do if they're spending all their time in a death match with insurgents.

Krauthammer also tells us that Iraq is already fighting a "civil war". As a semantic quibble, this is marvelous. As analysis, this is worthless. It's worth noting that a true Iraqi civil war, without heavy U.S. involvement, would have a very different character than what's going on now. The Sunni insurgents would stop fighting their current asymmetric war—whose goal seems to be to cause enough mayhem that the U.S. either leaves or respond with overwhelming force, thereby alienating a large swath of Sunnis—and instead try to fight a more conventional war in order to retake the entire country. If, even after Fallujah, they still have the weapons and manpower to do so, they could well win this; the Sunni insurgency is far better organized and equipped than the Iraqi National Guard and the rather raggedy Shia militias. In this scenario, the Kurds would probably break their de facto alliance with the Shia, cease all incursions into the Sunni triangle, and fall back to protect their oil interests in Kirkuk and Mosul. That could in turn lead to ethnic cleansing and other pleasantries. Whether the Sunnis could fight a two-front war capably is anyone's guess. Odds are, Iran would probably intervene on the side of the Shiites, though I doubt that's really the outcome we want.

There's a vast gap between what Krauthammer thinks "ought" to happen in Iraq and what is actually happening. The latter explains why we want to a) draw the Sunnis into politics and b) avoid having the Kurds and Shia simply "fight their own war".