Ratings systems are not a silver bullet either - they're often easy to game (products) or measure wrong things (restaurants); users can be pressured into giving a good rating (employee interaction rating machines at border control, which you have to press while still in front of the officer) or bosses can use them to control employees (a known not-exactly-a-taxi, semi-illegal company I won't name). Particular failure modes depend on small details about the rating system - whether it's immediate or delayed, anonymous or not, relevant to the other side's career or not, etc. - but there are always some.
Ratings and feedback in general are a good concept, but you can't just take a "SELECT AVG(rate) FROM policeman WHERE rate < 3" an run to the nearest CNN office to talk about how things are very bad. You have to stop and consider all issues of a given implementation of a rating system, and there are quite many of those.
I do agree that ratings can be gamed and are not a silver bullet though, that is true. It's difficult to get right.
The current situation is that citizens and police are stuck in a feedback loop of growing fear and resent towards each other. A key step to solving our problem is to contain this loop before it grows too strong. 'rrmm wrote about giving more visibility to the transgressions of policemen, but I argue that going for maximum publicity isn't always a best approach. Taking into the account how blindly people consume the media, I fear it may only exacerbate the vicious circle of fear and resent.
Sounds a lot like a 'no true Scotsman' fallacy.
Everything from apartments to restaurants to taxi and semi drivers have ratings or a feedback system and it hasn't brought any of those systems to a grinding halt.