The nature of baseball is that most players go through long slumps and bad seasons. I would hope that our knowlegeable fans would recognize that and restrain the booing. It really is a counter-productive example of self-indulgent venting. All it does is make the fan feel -- exactly what they feel I admit I don't know -- moral superiority? Class revenge? Do-your-job-itis? What are fans thinking, Turner is trying to do badly, or not trying hard enough?
For example, Chase Utley, one of my all-time favorite Phillies, had 10 consecutive years with RC+ from 110 to 150. But his worst year in that streak was 73 batting average points below his best, 66 OBP points below his best, and 141 SLG points below his best, meaning his OPS was off by more than 200 points. And yes, Phillies fans booed him that year.
When I see booing, most of the fans I notice are drunk and profane. I would hope it would just go away in Philly, but my guess is that won't ever, ever happen, sad to say.