This assumes the job of policing in the U.S. is, in fact, to enforce the law. It could also be several others things, such as raising funds for local governmen

This assumes the job of policing in the U.S. is, in fact, to enforce the law. It could also be several others things, such as raising funds for local government (primarily by targeting less privileged members of society). Another common argument is that they are primarily employed to reinforce existing power structures - See violence against anti-police violence protestors. Our government in general (and Supreme Court in particular) are loathe to put almost any limits on police behavior, or to enforce consequences for bad behavior. There is largely bi-partisan agreement on this, and the stranglehold the two-party system has on elections prevents alternatives.