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.
2015 (or was it 16?) Drew Doughty was as close to a flawless defenseman as we've seen since Lidstrom, and I think we were spoiled by that.
The biggest problems with Muzzin came from outside, as people looked at his 60% CF and didn't realize that he made few errors but egregious ones. But that's part of what made him so good, too--volume out of our zone and towards the net, good enough to keep checkers honest and away from Doughty as he was a threat on his own, and was ok taking some risks because the positive outweighed the negative. And being able to play 24 all-situation minutes to a net positive is a skill few NHL d-men possess, top-45-60 for sure. All defensemen make mistakes to be sure, but what kept Muzzin out of that upper echelon was the frequency and location of those mistakes. Not trying to over-emphasize it because it was still relatively rare, but the reason he'd take such a beating is people would forget two flawless periods of hockey when he flushed a centering pass right up the middle to no one.
Remember I"m one of his biggest defenders too. This example always makes me laugh because I remember it in real time going "please muzzin just eat it don't do what I think you're going to do" right before he does it
you can only see it at the very beginning here. Could just eat the puck or go behind the net but he throws it to a Shark for a quick 2-on-1 with Drew out of position expecting a pass:
MUFFIN
Edit: unrelatedly, "Quick robs Couture" brings up like 100 youtube videos
and maybe the most underrated save of all time