He didn't deserve to be fired, but he did because the team looks like a bunch of beer leaguers playing in the NHL. I think he deserves some blame for the way the Bruins are playing. They didn't take training camp seriously, they haven't practiced the PP, they can't make passes, they can't breakout with the puck, they can't get in position to shoot the puck in the offensive zone, they skate slow, they can't execute at all etc. etc. etc.
But a lot of that blame is on the players. Sacco is whatever, maybe they play better under him, but a lot of that is dependent on how the Bruins come out and play now that Monty is gone. For some on the team, they have quit on 3 coaches now. They don't deserve the benefit of doubt. If they continue to suck, Sweeney has to be let go so someone else can make the roster decisions.