There's another issue which you didn't specifically address: and that is the Democratic leadership (Reid, Pelosi, Dean, etc) basically dismissing calls for immediate withdrawal out of concern that the result would be complete chaos, civil war, loss of life, and basically an outcome entirely against US interests.

We cannot ignore this line of argument.

If we ignore this line of argument, all the MSM will say about the protests is "Nice sentiment. Unfortunately, regardless of the merits of starting the war, this is now a humanitarian situation which we cannot absolve ourselves of, neither for moral nor strategic reasons."

I propose three main inter-related counter-arguments to the MSM/Democratic leadership argument.

1) The conditions which could lead to civil war in Iraq likely will exist long after US troops leave at whatever date (assuming it's less than a decade or two). I believe the conditions are as follows: The Kurds and Shiites want at least limited autonomy, while the Sunnis who do not live in the resource-rich regions, don't want to be left behind financially as a result of the break-up of Iraq, and there are also non-resource-related territorial disputes. This is a problematic and volatile situation, and again, it's not likely to change once the Americans leave. Nor is it likely to be papered-over once a new government and military are established. This is a key point. I really doubt the Kurds, for instance, will want to permanently give up their dreams of autonomy. Look at the example of Turkey. Whatever national army gets formed could easily splinter along ethnic or sectarian lines. And I would say that such a scenario (splintering of the armed forces) is more likely under conditions that are not dictatorial (ie, under democratic conditions). One thing the US is clearly doing now is training and arming a new Iraqi army. Whatever civil war breaks out in the future will be all the more bloody in proportion to the degree of militarization and training of the splintered armed forces. So if civil war is to break out, it can happen now with all sides relatively unable to carry out massive attacks, or it can happen a little bit later with more heavily armed and trained soldiers, leading to more bloodshed.

2) We made a mistake when we invaded Iraq. It may not be a mistake we can "fix." We don't know how long it will take to "stabilize" the region. It may be decades. Can we afford (not just militarily and financially, but politically and morally) to stay there that long? Suppose the worst-case scenario happens (massive civil war as soon as the Americans leave), we could just chalk it up as a learning experience and use it as lesson as to one of the many reasons why killing tens of thousands of people (who never attacked us) to achieve political ends is a bad idea. It may be best to just cut our losses now. If a civil war does break out, there is no telling whether our troops could have prevented it by staying (come up with a number here) years there. Think about it. If we leave 12 years from now, and then civil war breaks out, William Kristol would probably just say it's because we were supposed to stay 13 years.

3) Given arguments 1 & 2 above, consider this: the longer we stay, the more animosity we generate, and the more radicalization and training we give to whatever jihadist terrorists or would-be terrorists taking advantage of the situation in Iraq. A lot of the bloodshed right now is a result of resistance to US occupation (as opposed to factional/sectarian violence). So it can be argued that the US is having as much of a destabilizing effect (which can be a factor leading to civil war) as any kind of stabilizing one.

Now if someone can stuff all of the above into a nifty, catchy slogan that can be read in a few seconds from a protest sign...