This is part of the problem across the board, IMO... Saying something like "Fuck the police." does a real disservice to the actual honest cops who are out there. There are some really horrible people out there, some of them wear badges. There are also some really good people out there, and some of them also wear badges.
Now there are certain places, like Chicago it seems, where there is a relatively low amount of oversight of the police and bad cops corrupt cops who don't stand up to it and the problem grows and gets out of control. IMO, cops need harsher punishments when they are found to be off the good path.
The problem is, the anti-police sentiment affects the good cops more than the bad ones. Bad cops just get angry at the sentiment and it makes them more prone to violence. Good cops get afraid of being reported on a bullshit charge that ends their career.