The Professor thinks the Iraq war was imprudent, but argues that it would be bad to cut and run. What person with an interest in the well-being of Americans or Iraqis can disagree, if "cutting and running" means some disorderly instant retreat. That would be bad.
But an orderly, staged withdrawal -- preferably requested by the Maliki government -- over a year or so would not be so bad. It would undercut the insurgency's principle point of recruitment. There are risks, but these are not eliminated by staying.
Peace in Iraq requires three things: co-option of elites from all parts of the sectarian/ethnic divide, removal of the occupation and suppression of those refusing to be co-opted.