It's bad on absolutely all fronts.
Firstly you're showing that you as a club don't respect players wish to leave. Of course he might have acted like a massive cnut and he hasn't really shown his commitment but I'd actually say that it's even more of a reason to flog him to Paris and forget he was even there. Besides we're not even certain whether he refused to travel with United because he's a bellend or maybe he'd been allowed to stay by the club because negotiations with PSG were already in advanced stage and we knew that he was going to leave anyway.
Secondly it's £45m we're talking about. We have potential investors, we're in stock exchange, it doesn't reflect greatly on the club to give up on that sort of money - which would boost our operating profit for annual period considerably - because we're willing to punish a player. If it was £10m then all right, maybe we could make an example out of him, but it's a considerable fee that could be used to sign at least two new players.
Eriksen might have made a bad decision to join Spurs but that's another matter. He was stagnating at Ajax and there seemed to be very little interest from top clubs though so he didn't really have much choice. Lamela I don't think was on the radar for any of the big clubs either.
Your views on Di Maria situation seem very weird on all fronts mate. You seem to think he's worth £50m and if PSG don't add that £5m or so to the fee then we should just act offended and give up on the whole fee, and use him as a squad player for reserves.
Maybe you're just annoyed at the whole thing