Are unions the prime determinants of police behavior?
As others here have said, the primary function of the police is to protect property rather than people. More specifically, it is to contain and repress the anxiety and anger caused by economic desperation. It is also to clear out low-income areas for gentrification, and broadly to police the borders between higher-income and poor parts of town. As the economy gets more unequal and a growing proportion of people fall into increasingly desperate economic straits, more and/or more aggressive policing is needed to accomplish this goal.