Keep this between us, but would a violent-but-short Shiite vs. Sunni civil war (in which the U.S. was not involved) be the worst thing that could happen? Just askin'! It might be the essential predicate to a rough ethnic and religious balance of power. Or it might produce a stable, de facto partition.
Well, it might not be the worst thing that could happen (from our perspective), but it would be very bad. However, from the Sunnis' perspective, it would be the worst thing that could happen, since they are growing increasingly unpopular as sponsors of / collaborators with terror attacks through Iraq -- and nobody liked them that much anyway. They're also growing militarily and economically weaker. Al Qaeda types like Zarqawi think that a massacre of Sunnis would galvanize the rest of the Arab (or at least Sunni) world, but that's got to look less likely as time passes and as Al Qaeda gets less popular inside and outside Iraq.
As WestHawk observes: "A full-blown sectarian civil war in Iraq would be bad for all, but it would be positively lethal for the Sunni position in Iraq. At the limit, they would be ethnically cleansed from the country. . . . It would be ugly to watch and bad for America's reputation, but few could say, in this scenario, that the Sunnis had not brought it on themselves." The Sunnis, I suspect, realize this, and old Ba'athist fantasies of omnipotence seem to be fading (Chemical Ali is said to be singing like a canary, along with several other Saddam cronies). If this is true, we'll see plenty of traditional brinksmanship but the Sunnis will always wind up making a deal, because the consequences of not making a deal will be too horrific. What's more, if they're smart, they'll recognize that holding out too long makes for a worse deal, as their position declines.
That's how it looks to me, anyway. Am I right? I don't know. I'm no Juan Cole or anything, but I could still be wrong.