Via GFR, James Fallows on why it's time for us to go. Leaving, he says, will likely lead to very bad events. But "If it is not in our power to prevent these disasters, then it is better to do as little extra damage to ourselves as possible before they occur." And it isn't in our power.
So the choice is between a terrible decision and one that is even worse. The terrible decision is just to begin leaving, knowing that even more innocent civilians will be killed and that we’ll be dealing with agitation out of Iraq for years to come. The worse decision would be to wait another year, or two, or three and then take that terrible course. If we thought a longer commitment and presence would lead to a better outcome, then the extra commitment might be sensible. But nothing occurring in Iraq in the last year has given rise to any hope that things are getting better rather than worse. (This, by the way, is the reason I have changed my mind: the absence of evidence that the chances for a “decent” departure will improve.)
Right. The trendlines are vital here. Staying would make sense if there were any reason to think staying longer would create the conditions for departing in the future under less screwed-up circumstances. All the evidence, however, is the reverse. Things are worse on 1 December 2006 than they were one year ago, worse than they were two years ago, worse than they were three years ago, and there's no reason to think that pattern is going to change.