[superuser2]

In principle it's not bad that police have an advocate. The union stops the brass from feeding random peons to the dogs to appease the mob. The union insists on adequate safety protections and working equipment. A mayor with a deficit to balance and an election to win might not provide them otherwise.

The problem is that the police's advocate is so much more powerful than its opponents. An adversarial legal system like ours breaks down when the adversaries aren't close to evenly matched.