I mean I guess it's what you deem as "wrong"... I personally think Pogba's tantrums that have spanned the better part of 2.5 years now are far, far more detrimental to the club than Lukaku's heavyhanded forcing of his transfer (not that I excuse that... just as a straight comparison). I think players like Pogba are protected a lot more due to their status and image (i.e. Ole will make excuses as to why Pogba misses trainings or flights for preseason, but with Rom he acts flabbergasted over the Anderlecht training). I also think Sanchez is effectively stealing wages from the club without any intention of putting in the necessary hard work to achieve the results and standards he needs at this point in his career... he doesn't even seem capable of staying fit longer than 3 weeks, and whilst I understand that there's only so much you can do about being injury prone, it doesn't appear that he's doing anything at all. I will admit that one could just be paranoia on my behalf though... There's every chance he's a model, hardworking professional... I just doubt it due to his reputation from Arsenal and the fact that he is a notoriously isolated member of the team.
Di Maria all but forced a transfer through too. Not to mention his week to week whinging about how much he detested Manchester and England in general.
Lingard though, is an absolute clown in my opinion. He is the player that most defaces the club. His actions are seldom monitored and he's given free reign to act like a total idiot (even if he does seem like quite a nice lad to be fair to him) whilst representing United. If you want to talk about professionalism (or lake thereof), then he is easily in a league of his own. He's, unfortunately for us, a marketable disgrace. But why that justifies him starting as many matches as he does, will never ever make sense to me... genuine lack of squad depth maybe?
Anyways, sorry to ramble. I just find it interesting that you feel so strongly about Rom but not about the other primadonnas in the squad. I guess Alexis is not really a prima donna but he is probably the closest thing we have to a mercenary operating in the team, and since he's not even a good one capable of executing his job well... I would personally quantify that as a lack of professionalism on his behalf also. If he took a wage cut it'd be a whole other story of course.