Bollocks. Maybe some let their personal opinion of his character cloud their judgement of him as a manager, maybe I'm one of them and just lack the self-awareness. But I'd also be willing to bet that what you argued against - others overlooking reality from being swept up in the myth of the man - is equally as true. What I will do is argue that there are valid reasons as to why he's not the right choice until I'm blue in the face.
It comes down to not believing Mourinho to be 'United material.' That's probably subjective bollocks which is difficult to argue one way or the other, but I believe there are footballing reasons to back it up.
To try to clear the more personal/subjective reasons out the way first: Mourinho is the 'perfect choice', if all that matters is winning trophies. I think there's a decent argument to be made for him coming in for a couple of years immediately after Ferguson to steady the ship, but I'd be worried at what cost to the club that would be. Whether it is bollocks or not, I believe that this club has a unique identity. Mourinho acts the utter bastard but everyone forgives him because he's a winner, the biggest kind - a self-aggrandising one (I cannot believe that you are anyone else could type with a straight face: 'he's also not that much of a cnut'). I think he'd cause the club damage coming here. People always reply that Fergie is a bastard too but I see differences, though again you may well be right that this is personal bias. Just because you have a manager who is a bastard doesn't mean you should replace him with another though. Ferguson has only hurt this club through personal bollocks a couple of times, I'm thinking mainly the Rock of Gibraltar fiasco. He'd given enough to the club by that time to be forgiven (again about winning). All his other bastardry is done for the benefit of the club. Mourinho is exactly the same but ramped up even further. That in itself is not a bad thing, but I think Fergie gets away with it because of his position in the game. He is the godfather of English football, his relationship with those in the game, the press, allows him to take certain liberties. Mourinho doesn't have that. Maybe he could tone it down in the future to an acceptable level, but he's turned every club he's managed at into a circus. You look at public opinion when he poked Vilanova in the eye (can anyone give an example of Ferguson ever doing anything like that?) and pretty much no-one wanted him here. Now he's going to win the title, it's all changed. People forgive winners anything. I just don't think winning is enough at United.
You look at the clubs he has been at (I don't know enough about the position at Porto at the time): Chelsea, Inter, Madrid - all were desperate for success with a win-now mentality. Abramovich wanted instant glory, Inter needed to crack Europe with their one last shot, Madrid who are usually more like us needed an instant fix to break Barca's monopoly. I don't think he gets the Madrid job if Madrid had had a winning side the last few years.
I don't think this 'burnout' issue after he leaves is all rubbish. For sure it's used as a weak excuse by managers following him in who can't match his management. But it's also because Mourinho has always been about win-now. Sustained success is the hardest thing in football, just look out our title challengers or Barca now. Mourinho is unproven in this regard but that alone is not reason enough to give him the job. He also stays for short stints because he alienates pretty much everyone wherever he goes, except of course the club's supporters and players, because he delivers that instant success people crave. You might think what else matters, but if you're planning for long-term success, you don't want your manager pissing off just about everyone in positions of power within the club, within the game, the media. Would Mourinho have handled our ownership situation in the same way Fergie has? Could we be looking at a similar situation to Chelsea (or a lesser extent Inter) in terms of player power, after his time here? I feel we're already halfway there with our dealings with Mendes, but what effect would Mourinho have on our leadership structure? There's a very good chance that Madrid will have serious issues when Mourinho leaves and that will not just be down to the absence of his coaching. I don't think any one figure is worth the trouble he brings.