My principle issue with Sassaman is his role in the Samarra bridge incident. His tactics, strategy, and general approach to COIN has its merits and drawbacks. My admittedly limited knowledge of the intimate details of his BN's operations leads me to believe that his approach was wrong-headed, but I don't think it was egregiously or intentionally immoral.
But I think he was unequivocally wrong in encouraging (or instructing?) his subordinates to lie about the bridge incident. It is bad practice in COIN to not admit openly and fully to mistakes made, and more importantly, it flies in the face of the Army values of honor and integrity. Sassaman should have at bare minimum instructed his men to tell the truth, and really should have protected his subordinates not by lying for them, but by taking more responsibility himself. I think his failure does show a profound lack of morality and ethics and I think he does deserve to be punished for those failings.