Best Case Scenarios Failed; Time to Trot Out the Worst-Case Scenarios

One of the most drearily fascinating things about this country's Bush-dictated six-year obsession with Iraq (as if it were the only country in the Mid-East, or the world, that mattered, as if Pakistan wasn't the "safe harbor" we were trying to prevent from occurring a thousand miles west) is the early addiction to best-case scenarios. Thomas Ricks' book Fiasco highlights, like a funereal leitmotif, the proclivity of decision-makers at all levels of the administration to buy the assumptions of Plan A, and therefore to reject even the need for Plans B, C, or D. The public was treated to years of best-case scenarios -- grateful Iraqis strewing occupying Americans with flowers, oil revenues paying for the reconstruction, a cakewalk -- all of which were followed by something far less rosy.

Now the time comes for staving off calls for ending this nightmare, and the same people have flipped their polarizing lenses, spewing an unending series of worst-case scenarios, pushing dire predictions of humanitarian and geopolitical catastrophe if the US withdraws its troops.

My question: if such folks (who include John McCain) were so wrong with their best-case scenarios, why should we accord any credibility to their worst-case ones?