They signed up for the job of violently enforcing existing power structures.

It's due to their function. Lots of people make the mistake of viewing it as a moral category and judge each cop individually as a result rather than as an organ of capitalist state power, and their own survival hinges on fulfilling this function and following state orders (because wage labor).

John from your neighborhood might be a nice guy and a good cop, but if there's ever a serious enough general strike, he'll be there to beat up the workers.

Their job is to enforce the current social order and its power relations and in accordance with that ally and are protected from consequences by the the bourgeois as they do their job of helping them remain in power.

Origin, training, hiring practices, lack of accountability, militarization.... there are so many reasons, honestly. Its hard to pick one because its more like a convergence than a singular root cause.

Edit: You know what? I'm going to revise my answer.

Capitalism. Final answer.

The stereotypical role nowadays is a position where you are given authority over most people (in certain scenarios at least) and that draws in people with a particular psychology.

Give a certain type of person power.

I mean, in America, it did start out to catch runaway slaves. So, I guess protecting private property has always been there thing. They just tried to have PR branding in the 70s that they serve and protect communities. False.

Well, if you watch body cam stuff on the tubes. It's definitely not universal. There are some really good cops and then motherfucking wastes of life caught planting drugs and lying and even killing presumably innocent people ...

Lack of training and a dangerous work environment, paired with lack of accountability.

This is not the root cause, but exacerbates the problem: the majority of them are juicing. Steroids. Makes a person aggressive if the situation is correct for it.

Root cause? Capitalism.

Their position of protecting property and not people, simple as. People who choose people over property, do not become cops. It is a simple filter that selects for bastards.

I think there’s a few forces at work here on more personal levels.

1. A lot cops are veterans which means their background is focused on the use of force to rapidly end situations, which also means a lot of encounters are escalated quickly rather than de-escalated or prolonged via non-resolving techniques (i.e., conversation rather than just cuffing the person). Especially in countries that participated in the so-called GWOT they’re background is counter-insurgency so they’re trained to approach every environment being one that could immediately turn into a firefight and approach all situations like that.
2. A lot of cops are armed. Something about how if you have a hammer everything’s a nail…
3. They’re often true believers. Capital does deserve to be protected. Property deserves to be protected. Men with long hair are lazy hippies, and minorities (whoever that is in the context) are dehumanized outsiders. Cops are often personally reactionary: politically conservative, actively religious people who simply believe in the existing order.
4. Some just don’t give a shit and want the perks. Cops get their metaphorical dick sucked on a daily basis by basically everybody in politics and public life. They get sweet perks. They’re literally immune in same jurisdictions. That’s got to feel good.
5. Some of them are just bastards, but in a different way from points 3 or 4. Think of the Pinkertons shooting strikers: some were covered as true believers or like the other perks, but some just specifically like killing. How many Kyle Rittenhouses’s have become cops just to seek violence?

But fundamentally, they’re bastards even because if they aren’t true believers, it’s their job to blindly enforce laws. They’re literally paid to dissociate from any personal moral compass they may claim to have and just be an impersonal jackboot for the state. The job description of a cop is to follow orders, no questions asked. That’ll make anybody act the bastard.

Because they're granted a monopoly on violence by the state, and exercise that right.

A lot of people posting stuff which is not wrong but im going to post another smaller piece here as well. People who go into the job are a particular type of personality and the hiring and training process further weeds out the unlike kind. But then on top of all of that they tend to only see the very worst in our society as well. Which then as the ones who survive begin training the new the training gets more skewed to protecting against that worst kind. Its a negative feedback loop.

That is not to say what others have said is wrong. Its just not one specific thing and the type of person able to survive in that job without being killed or killing themselves does not garner the type of person we as a society would like to have working that job.

Their job is to deal with criminals, to see crime, to find crime, to fill a quota of crime stopped.

But the thing is that crime can't be eradicated. As long as there are people who want to control, people who want to exploit loopholes around that which is controlled and people who just don't give a fuck, being a police officer is a thankless job and an unavoidable spiral towards falling into the worst this world has to offer.

Every bad thing you can think of, they have to deal with preventing it, seeing it happen or settling the aftermath. And it gets to them. It gets to everyone.

Like, every bad news we see here, reading or watching it from a screen, they deal with them every day, live. And you can see how much it affects people here, let alone those directly involved.

The life of a police officer is not a happy one. It's not a stable one. It's not a safe one. They live in (paranoid) fear that every criminal they meet might have a gun or a knife and will attack them. They see the results of every assault or accident and have to live through the powerlessness of being unable to change it. They are the poster child of what happens when you give a gun and a position of power to someone who's depressed or suffering PTSD.

The ugly truth is you don't want to be a police officer because it will absolutely fuck you up.