I have seen unfair criticism, and fair criticism leveled at almost every player on the roster. I do it sometimes as well. I think unfair criticism was more prevalent with Muzzin. It is the nature of message boards, some posters find a whipping boy and others pile on for mistakes they would let slide with other players. Sometimes it was even Muzzin trying to cover for a mistake made be a teammate, but since he was the last line of defense he received the blame.
Every defenseman in the NHL who is not a superstar makes poor decisions from time to time. Muzzin was criticized quite a bit this season, yet he was one of the few players on the roster with a positive plus/minus.