To play devil's advocate, I'd point out that police in the US face a rather unique situation, in that so much of the general population is armed with lethal weaponry. Over here in kangaroo land, nobody owns guns, barring those that use them for agricultural purposes or sport. We've got fairly strict gun control laws. Your average cop doesn't need to be worried about getting shot when they pull someone over.
In the US, they face the constant risk of gun violence. Thus, they're trained to deal with that, which is essentially military training. Little wonder they act like it.
Perhaps if people weren't allowed to own guns in the US, there'd be less violence? Training time spent on avoiding getting shot could be spent on deescalation techniques?
As I posted in this thread;
http://www.bay12forums.com/smf/index.php?topic=176557.msg8148974#msg8148974 Violence caused by police are a multifacted problem. There was not a high rate of police shootings of civilians until after the militarization of the police in the US. This has been a gradual trend over the last half-century or so - both of lowering of standards for police training, a move away from de-escalation training, and an overall increase of "us-vs-them" mentality amongst the police. Furthermore, the justice system has been corrupted by prosecutors backed by for-profit prisons, and a distinct lack of accountability among the police - given the same department they work at would be the ones investigating any crimes an individual officer commits, as well as often the same judges some of these officers will have worked with for years or even decades, leads to a great deal of nepotism.
The only realistic means to change that is to
1. Enforce federal standards for police training and psychological screening,
2. Eliminate for-profit prisons and the drug war,
3. Elevate any crimes committed by police officers to that of federal statute, and thus being directly overseen by federal courts,
4. Ensure any crimes to which a police officer is suspected of is investigated by a federal body like the FBI.
Quite honestly, citizens owning guns is not as much an issue in the US, at least as far as people legally permitted to own firearms are concerned. In fact, people who go through the measure to get a concealed carry licence in the USA are less likely to commit a crime than a police officer, which should say something to the measure in which there is actual accountability. Even beyond concealed carry, more than 2/3rds of gun violence are carried out by people who are not legally able to have a gun. Part of the problem in the USA, where that's concerned, is "felon with a firearm", itself a felony that can carry a multiple year sentence, is very rarely prosecuted. Less than 1% of failed background checks are actually investigated by the police, and if I remember the figure correctly, around 20% of said rejections are from prohibited persons who are themselves breaking the law even attempting to get a firearm even as they are denied, meaning we have millions of people each year trying to get firearms illegally who the police just... ignore.
Of course, if you were caught using cannabis before you were an adult and later the police learn you own firearms, the police might decide you're such a threat to society and they will skip even no-knock raids and fire into your bedroom from the curbside to kill you because you stood up and started walking towards the door, then proceed to refuse to even show a warrant after the fact to your family for the next 3 months+. But this falls back into where police officer's priorities stand - they gain more for getting people for a 2-8 year sentence of drug possession than going after a 1-2 year sentence for felons having firearms, and prosecutors are more likely to win a plea bargain for such than say, armed robbery or assault, so police in the USA far more aggressively go after any sort of drug offences than other crimes, as that's where they get the most bonuses from. Sadly, so many officers just see what they're doing as nothing more than a job, take as few risks to themselves as they can, and just try to maximize the money they can make, which leads to others suffering for it.