I trust that by now everyone's already read Kevin Drum's two mini-essays on the rise of the chaos hawks who warn "that if we leave Iraq the entire Middle East will go up in flames."
The only thing I would add is that it's worth looking at this phenomenon, at least in part, through the perspective that to many people the real risk may be that if we leave Iraq the entire Middle East might not go up in flames. We've shifted back and forth from the Shah to Saddam to "dual containment" to regime change to stay the course to "surge" over the decades all on the premise that American domination of the Persian Gulf is vitally necessary in order to prevent something terrible from happening.
What if we get chased out and things turn out to be non-catastrophic? What if bloodshed is limited to Iraq and maybe some areas around the Kurdistan-Turkey border that nobody cares about? What if oil keeps flowing? What if it turns out that, a Shiite-dominated government isn't interested in the kind of pan-Arabist ideology that could make Iraq a threat to Kuwait and Saudi Arabia? What if it also turns out that it's not really feasible for a Persian regime in Teheran to control Iraq? And what if Taliban-style governance and global holy war turn out to be really unpopular?
What, in short, if things turn out to be basically okay for America and for Americans? Well, that'd be good, it seems to me. But it would also call into question a lot of habits of mind, past policies, spending commitments, career paths, sacred cows, delusions of grandeur, etc. That, I think, is why relatively few people in Washington seem interested in entertaining optimistic scenarios about the regional context even though an optimistic scenario seems more likely to me than do frequently discussed worst-case scenarios. The truth of the matter, though, is that there hasn't been a moment when the United States didn't try to micromanage events in the Gulf since, well, since the British Empire was doing it instead. There isn't, however, much in the way of evidence that this kind of policy is actually necessary. It does, however, seem to have succeeded in producing one of the most politically screwed up places on the planet.