I'll admit, it's a little dumb. But I just don't like him as a person, seeing him on tv and such. But mostly I feel like the Red Sox needed someone stable after the circus that last season ended up being, and Valentine is/was a fiery dude that shoots off his mouth a bit much and butts heads with GMs. But thats all my opinion, I'm just not a Valentine fan.
I'm not in awe of Valentine and did not think he was the obvious manager, but he does have a few things going for him. First, he'll call out loafers and have the stature to stand up to vets. As you put it, the team was disfunctional down the stretch, and everyone, including Francona, said they needed a kick in the butt. One reason Francona left he says is he did not think he was the right guy to do it due to his history with the players. Second, for an older manager, they say he is very statistically oriented. He was an early adopter of some of Bill James's ideas, so it is likely he can deal with input from James and others in the Red Sox operations department. That said, he has the stature to tell them to f'off if he feels something will not work. Third, it probably would not take much to be better than Francona at this, but he is a knowledgeable in game manager. His problem always was warring with his GM and owners and not his game managing. If I'm Cherington, then I watch my back, especially since this guy is Lucchino's choice. Bottom line is Farrell was not available, Mills has not shown much in Houston, and Hale was too closely tied to the 2011 season to be the change they were looking for. IF Valentine works, then great. If he doesn't, Farrell will have his contract run out soon.