The problem is the police (cops) do not serve the people any more. They serve the politicians. The politicians of a corrupt and broken system. Therefore, given the various localities around the country, the general amount of 'corruption and break' in the police system is proportionate to the local political and financial structure.
To say that 'all cops are assholes' is an incorrect assumption, however depending on the local system it could be such a system where the people who want to be cops are assholes. Doing so not only establishes a regional 'persona' of what a cop should be/do/think and that persona is generally held by the hiring process of the region.
The persona of local police becomes the institution with Police Unions and all the 'together' stuff the on the job people do. So yes the thin blue line does become an institution, literally and figuratively in many places.
I'll take the small town Iowa cops over the Dallas Tx cops any day of the week. Nebraska cops and Missouri cops were about the same, Florida cops are assholes across the board. The bigger problem is that who the majority of localities serve is no longer the people, it often a politician and their interests not necessarily the letter or the spirit of the law.
As to their humanity, of course they're human. They also chose a job which puts them in a position, and a smart person would recognize this, where they would be required to act unethically and possibly immorally because a corrupt controlling structure, government. They still made the the choice to pursue said career. So to say that they themselves are not to blame is also incorrect. Army soldiers are trained, conditioned, and coached on how to kill indiscriminately and are expected to do so if called upon by the government. Police forces are no different, they are expected to uphold the law regardless of it's ethical or moral validity or lack thereof. To say that they themselves are not in part responsible for those actions is to say that an enlisted Nazi soldier was not responsible for the atrocities he committed in the name of his job.
In short, nearly all cops are assholes because nearly every political and financial structure in the country is based on greed, back room deals, and dishonesty. They are simply the current chosen weapon of the establishment, but to excuse them because they didn't accurately judge the ethical and moral ramifications of their chosen profession makes no sense at all. Ignorance of the morality of your profession is not a hall pass to be an asshole.
Cops = Governmental weapon
Pot Smokers = Shooting Gallery for the government
any questions?