I don't really know much of his supposed bitterness as a pundit, but at the time when he told the media that he was treated like a "guinea pig", the tabloids did their best to take the quotes out of context and create the illusion of tension between Hargreaves and United. The complete interview (which the tabloids twisted quotes from) from the Guardian had nothing of the sort. He came across as very sad that it didn't work out at United, but quite clearly frustrated at the injury. By his own admission, he seems to take a share of the blame, because his eagerness to overcome the injury and to play occasionally set him back. He did state that the treatment he received from City's medical staff was much better than at United, but I would very much doubt he's saying that out of spite. I remember him still being very complimentary to the staff at United.
The tabloids seemed to have done a good job of giving Hargreaves the reputation of being bitter towards United, because whenever Hargreaves says anything realistic about United now, such as not really having much of a chance of winning the league or the Champions League, it's usually because he's bitter, and not because there are other teams who are much better than us.
Fans probably need to stop being so precious, and accept that not all ex-United players are going to blindly defend the club when they are doing a job which requires them to be impartial.
