I'm curious as to why you think an immediate US troop withdrawal would be "foolish and shortsighted" and in contradiction to "an honest assessment of the reality".
My own sense is that the threat of civil war is overblown, and has been used to justify the occupation. There seems to be more evidence, including from the recent uprising, that the different religious and ethnic factions accept the idea of a federated Iraq, and that the demands of the world economy and of regional powers like Turkey and Iran will act as further constraints against fissiparous tendencies. Differences that have emerged over religious influence in public life or that will emerge over the division of resource revenues are normal and containable within parliamentary regimes. All this is quite apart from the fact that the international community, even if it wanted to, can't really regulate historical development, which is by nature a messy process, and that when interventions have been undertaken, they have been directed at the protection of US and broader Western interests, and have not addressed the broader "humanitarian" and democratic goals of wishful liberals. In the case of Iraq, the US-led invasion and occupation has, in fact, been enormously destabilizing. In light of the above, what "consequences" of an American withdrawal are you particularly concerned about?
Marv Gandall