There's alot to unpick here.
A- Maguire is a half decent CB. Sure he lacks the pace to play in a high line, he needs someone to do the thinking for him as he lacks ability to scan what's happening around him and positioning and he's certainly no captain however he's not Phil Jones. The guy is built like a rock which makes him physically imposing, he's good in air, he rarely gives away ball possession (mainly because he plays safe) and on top of that he never gets injured. He'd be a great asset in a team that defends in numbers and plays in a deep line which mean nearly all EPL sides (bar top 6) and Serie A clubs
B- Maguire will always be more noticed then anyone else. He's our captain, he's the most expensive CB in the world and the cornerstone on which England's national team's defence is built upon. We all know that the majority of pundits are pro England and the fact that Maguire is stuck on the bench is bad news for them and the nation. They will keep him relevant.
C- These 'leaks' are definitely coming from Maguire's camp else he would rubbish them. Its also consistent to what he had done prior with his agent telling Rio to back off
D- Its within Maguire's interest to up the pressure. Players who stay silent while sitting on the bench ends up like VDB or Phil Jones. Maguire is too big for that (England int, United captain, most expensive defender etc). There's no such thing as bad publicity and if we're dead set in not giving him first team football then its only plausible for him to stink the whole place up until the club sells him for next to nothing. That (+B) has its own set of consequences as the more he or his mates in the media engage into this tactic, the more he'll piss fans off who will turn on him more. No one gives a feck about what a reserve player think especially one who had proved himself to be a big waste of money.
E- United supporters are United supporters not this or that player supporters. Actually United's decline is partly down to us protecting players far too much (Jones, Shaw, Lingard, Welback etc)
Conclusion - Maguire needs to leave and we need to sell him ASAP. Else this will end up badly (more leaks, more media scrutiny, every defeat being blamed for us not playing Maguire etc).