The principle here is about respecting your employer. It doesn't matter whether you earn 20 grand a year or 500 grand a week. I believe you should show respect to the hand that feeds you. Not only has he done an interview in secret, he has slagged off the owners, the manager, former players and the entire club infrastructure to a bloke like Piers Morgan, who would sell a story about his own Mum to make headlines.
Its a terrible look.
The criticism of Man U from the former players / Manager you mention came largely after they left and are not on the same page as Ronaldo's comments.