I think a lot of it was related to society unnecessarily trying to control and micromanage different areas of people's lives. Prohibition was a mistake, and it led to the rise of organized crime, which the politicians and police turned the blind eye to, which allowed it to flourish.
That kind of corruption may have contributed to a greater sense of cynicism which arose in the 50s and 60s, as well as growing dissatisfaction over civil rights and the government's paranoid delusions about "enemies" all over the world. This likely also led to an increased lack of faith in the system and those who work for it.
The motorized culture might have also contributed to public attitudes about police officers. Police and local governments also became larger, which necessitated greater revenue, which then turned cops from friendly arbiters walking a beat into obsessive, bureaucratic, pettifogging martinets, ready to write citations and issue fines for every conceivable petty violation out there.
There's a popular theme in popular culture which might often pit the "outlaw speeder" against the cop(s) trying to stop them. At best, the traffic violator is seen as a hero, while the cops are seen as killjoys who are only out to spoil everyone's fun - just because they can. Or it might be a case of fun-loving kids just wanting to party, while cops are seen as some kind of nemesis.
Another significant aspect of all of this is that, in America, we're taught almost literally from birth that we are the greatest country on Earth, far better than other countries because we're so "free" and have a commitment to human rights.
We're told that we can do anything we want, as long as we don't hurt or violate the rights of other people. Kids are told this over and over and over again, in school, in church, from their parents and other adults, from TV, from politicians. Even kids who can barely write their own name somehow manage to learn in school that they have rights (even if they don't learn anything else).
That's where the "I want to do what I want to do" comes from. People are conditioned and inculcated with this idea practically from birth. So, when cops come along and ostensibly violate these principles of America's Founding, it shatters the false image of a "free country" and is almost seen as a kind of treachery and betrayal on the part of the cops. Someone might say, "We were told that we live in a free country, yet these cops don't seem to understand it."
It's these kinds of inconsistencies and contradictions which lead to disrespect of the law and those who enforce it. To me, the onus is on the politicians, lawyers, and cops to fix this, so the system isn't seen as some kind of ad hoc mish-mash of frivolity, hypocrisy, and emotional chaos.
In other words, if police don't like being called "fascists," they need to stop acting like it. They need to do their job in accordance with the principles laid down by America's Founders, which cherish human rights, freedom, liberty, and justice for all.
An example of what I would consider a "good cop" would be the character of Odo from Star Trek: Deep Space 9. He would sometimes ignore the letter of the law if there were higher principles of justice and morality at stake. Cops might be able to achieve better results if they'd take their nose out of the rule book and take a long hard look at what surrounds them.
When you condemn police officers generally, as you have, you are making accusations against me, and I take it just as personally as a Black person would if you said all Blacks are lazy.
Blanket statements like this is pure nonsense, decidedly false.
The politicians make the laws, the people elect the politicians. The police enforce the law, layers litigate the law.
So, ultimately, it is the responsibility of the people to correct the law if they don't like it.
Your pontificating about human rights, freedom, liberty and justice for all is a fine bit of rhetoric. However, every arrest made is because one or more people is denying someone else their rights, freedom, and liberty.
So, you want the police to ignore the letter of the law. For who? Whites, Blacks, left handed people, everybody?
Every time I have ignored "the letter of the law", and I have, numerous times, based upon my own judgement I created two problems.
1) I was not responsible for being a judge, that was not part of my remit when it comes to the law. What if my personal judgement was different than yours, since you imply you could do better. You would still complain, right?
2) Every time I opted for selective enforcement, the next guy I arrested for the same offense was being treated more harshly than the last guy. Fair?
Police Officers are infinitely more tuned into what is going on around them than you are.
Bottom line, you want to make a police officer a gumby to twist into any configuration you think is best.
This is what many demand, we want exemptions based upon our politics, race, gender, whatever.
Sadly, you are getting your wish in some cities. ANTIFA can virtually take control of downtown Portland when they choose, and the police loosely enforce perimeters, yet make no effort to stop the law breaking within the perimeter. You might remember the Conservative reporter who met the criteria of being great by the left, he was a homosexual, and a member of a minority race. However, he is a Conservative, hated by ANTIFA, and they beat the hell out of him and stole his camera, and THE POLICE JUST WATCHED, because they were under orders not to intercede.
This is what happens when policing becomes the victim of of political wars and radical governments. This is the ugly side of selective enforcement, and there is your true fascism.
Politicians have always put pressure on the Police for their advantage, but it is occurring in some jurisdictions in a very alarming fashion. The enforcement of the law is thrown out the window.