There are also all sorts of rules that are learned on the job and aren't not in any manual. Ways for maintaining control and authority mostly. Many of these practices are unsanctioned and unofficial, but still essential for being able to do the job. Some things are both crucial and illegal.
Cops usually feel like when they get busted for being arrogant, bullying or outright violence that they are are victims of these situations. They do what everyone does, what has to be done for policing to be viable. Those pencil pushers with their removed perspective are making judgments about their irrelevant rules being broken.
They are under stress. Violence is a part of their days. Most of the people they deal with are lowlifes, lyres, cheaters. There is real stress. Real danger
That said, a lot of these practices aren't benign and they aren't inevitable. The police does genuinely attract many problematic people and it makes other. They get used to defending their authority and meet challenges to it with extreme responses. They develop a cops & robbers, us & them worldview that becomes their reality. More specifically cops, criminals and naive spectators, citizens & bureaucrats.
They develop a bullying mannerism.
Police manage to do their jobs without guns at all in many places. They deal with violent crime just like cops in the states. I'm not saying this should be adopted by US department, but is proof that there are other ways of doing things.
I think lights good for the paradigm. But, whatever that light reveals needs to be dealt with. Maybe police modus operandi needs to changed. But, maybe the rulebook needs to change too. It can be dangerous trying to enforce the official rulebook after long periods where it has only been enforced selectively. Maybe the official way of doing things doesn't work.
That said, this following cops around only plays to the problem paradigm. It's harassment, like what paparazzi do. It's belligerent. Maybe it's valuable as a protest, but it isn't as solution.
What I think should happen in law enforcement is that everything should be recorded. Every interrogation. Every arrest. Every time a cop pulls you over. This is all evidence and it should be part of every booking.
Hopefully that will make the need for this sort of thing go away.