Of course they do some good. You could improve things even further by implementing a system like Judge Dredd, and we'd save a ton of money as well.

This is the problem with limits on law enforcement. There are tradeoffs, and people really don't like tradeoffs. Many people prefer to just assume that law enforcement will use their powers for good, rather than have to think about whether any given change will do more harm than good due to enabling bad law enforcement.