I don't believe that any side of Michael was 'sadistic'. I feel that from the moment he lost Appolonia, a certain degree of numbness took over, that even Kay couldn't break...and everything he did or said in terms of business from then on was well calculated and devoid of emotion. He neither liked nor disliked the way he dealt with any of his enemies...(even with Fredo, who was not merely an enemy but a traitor which in a way is worse)...he just percieved it as what needed to be done to protect 'The Family'.

The one kindness he showed in ordering that Fredo be unharmed while their mother was alive...had nothing to do with 'business', nothing to do with Fredo. It was for his mother (albeit via the insistence of M. Puzo).

Apple