Assessing the opposition: who is in league with whom, and how can we expect them to behave in the wake of a withdrawal? As I understand it, al Qaeda-style terrorists comprise a small percentage of the Iraqi outlaws, and they are the ones WE should be most concerned about, if not exclusively concerned about. They are our sworn enemies, with a track record. Their ability to use an Iraq-after-withdrawal as a safe-haven, a launching-pad, a training-camp center, a weapons-lab refuge and the like should be our main (only?) concern. Yet, will that horror develop in the wake of a withdrawal? The other components of the Iraqi opposition fall into three general categories: the Sunni (Ba'athist) insurgents; the sectarian militia, and those concerned with nonpolitical criminal activities.
None of these latter three groups, however, have any particular gripe with the US, but only with its occupation of Iraq. Well, the criminals don't even care about that, particularly. The Sunnis want a share of oil revenue and either an autonomous, federated region or a meaningful voice in running the country. Their interest in killing Americans extends only as far as the occupation lasts, I suggest, for the reason that the Americans ousted their government and enable its replacement to function with policies disadvantageous to their group. On the other hand, the sectarians, a more mysterious set of groupings as far as motivations go, seem to draw strength from resistance to the government and its Shi'ite loyalties (the Sunni sectarians), a frank religious motivation to establish an Islamic state (some Shi'ite sectarians), and a pan-Shi'ite drive fueled by Iran and aimed at either unity with it or a close, close alliance (other Shi'ite sectarians; the latter two groups overlap). From these latter two groups, the danger to America is more diffuse than it is with al-Qaeda: a general animosity to the "Great Satan," but not yet a jihad.
The question is how much will these latter groups (excluding al-Qaeda) tolerate a "terroist base" within the country. I assume that with the dissolution of the occupation, Sunni-insurgent ire towards America will wane significantly, with not pose a problem for us. I also assume that Shi'ite sectarianism will be subsumed under our policy towards Iran, and will not present a significant problem independent of it. So, how can true anti-American terrorists be expected to fare in Iraq post-occupation?
The other elephant in the room is how all these groups will behave in the wake of a withdrawal. Can we expect a bloodbath, an outright civil war, a contagious chaos? How many lives will be negatively impacted? Can we even prevent these nightmares by remaining in-country in force? And, importantly, how much would we be morally responsible for a worst-case outcome, if we left, due to our role in toppling the vicious, oppressive regime that held all these forces in check?