Personally, I would never boo a player in a United shirt but people pay their money to go and watch and they're entitled to their opinion, whether or not we agree with it, we can't tell other people how they should consume football or behave.
I think in Ali's case, you could clearly see there was something wrong with him on a personal level, he just dropped off massively with no real explanation. Whereas with Maguire he kind of brings the attention on himself, he makes too many errors for a CB and more often than not, it leads to a goal, then he comes out and tells everyone they need to do better or cups his ears to the crowd when he scores against Gillingham. In his case he really should just take a step back and focus on cutting out the mistakes instead of trying to be prime Beckenbauer. No one wants him at the half way line missing tackles and giving the ball away, we want him in the box winning headers, blocking shots, and making challenges (on the opposition, not his own players).
It seems like he's too stupid or stubborn to accept his reality sometimes, I think that's why it's open season on him and has been for a while.
