If there were gangs out killing cops, they would not be in need of an application like Waze to do it. The two NYC cops that were killed a couple months ago were not tracked by anything. The killings were by what appears to be a vigilante that wanted to kill "any" cop.
They psychology behind that is a different thread and story, but the point about being "tracked" is valid. Cops drive in marked cars and wear uniforms. Someone actually "hunting" them would not need an application. In fact it would probably be stupid to do so, because of all the data the application tracking (it would limit suspects).
I also said that it wouldn't make any difference in reality, if you read my post to the end, to take the functionality out of waze.
That being said, such an app could be used to find isolated groups of police (i.e. middle of the night speed traps in the middle of nowhere) to attack which means that the idea is not completely invalid.
There is no shortage of stupid or tech ignorant people in the world so I wouldn't exactly use that as a proof that people would not use an app to find police to attack.