First, that's fair enough, although I don't think clubs usually ask opinions from everyone before signing new players. Maybe the context here is different but, in my (humble and worthless in reality) opinion, the usual chain of decision-making for all players should be applied in this case.
Secondly, I expect them to do that for good PR but that doesn't necessarily mean a lot privately as they failed to do the same for Antony as I would have expected them to do for the sake of coherence.
Thirdly, United deals with more circus than MG would bring, that I'm quite sure. The relative silence over him in Spain and even talks of bigger clubs being interested makes me think we overestimate this effect of bringing him back, maybe I'm wrong.
Lastly, like I said, he's not a senior player so can't be seen as a role model fot the younger ones. Also, his career has gone through so much at such a young age that I don't think any of them can see him as getting away with anything. CR seems to have gotten away with similar stuff, yet I don't think it necessarily affects younger players around him in his different clubs.
And yes, redemption can be anywhere, that I agree, only I think it can also be here, and I wouldn't mind it.