I for one do believe that is their primary function. However good intentions don't justify violating our rights or accepting the (demonstrated) potential for abuse.

It might be their intended use (from a police department's perspective), but it's certainly not their intended function.

Flock collects these images, and uses them to train statistical models, and sells those models to police departments as a one-click crime solving solution.

That means that their primary function is to passively aggregate driver behavior into an automated judgement system, where the entire judicial system (designed to check and balance itself) is laundered away. Flock cameras exist to fundamentally replace police work, not to assist with it.