From my perspective, and the way I was taught in two different police academies and years of police work (under California law), A police officer (or a citizen) may not use deadly force solely in defense of property. Burglary, auto theft, etc. No shooting at moving vehicles, even if it's coming at you. (Unless you can't get out of the way and it's life threatening) No deadly force against rioters or looters unless in self defense or when defending the life of another, unless: the crime committed is so great that it would be justified to use deadly force to prevent a suspect's escape or to prevent the crime. And the threat must be actual, not just perceived, coupled with a present ability to cause death or GBI (Great bodily injury) Murder, attempted murder, assault with a deadly weapon etc.
Arson is one of those iffy, borderline areas because fire behavior is often deadly unpredictable. No furtive movement excuses "I thought he reached for a gun" No sorry, that won't fly. You better see the darn gun and not a "drop gun" either. And: No shooting of fleeing felons, unless to prevent the escape of a violent felony suspect: Rape, armed robbery, kidnapping and the other violent felonies mentioned above. AND ABOVE ALL: No unnecessary "probable cause" shootings. Don't shoot somebody just because they are "bought and paid for" Just because there is legal justification to do so. We were taught to disarm suspects not shoot them. I was also taught, If you have to use force when making an arrest, make darn sure it's justified and according to the law: "Only that force which is necessary to effect the arrest"
Police officers are expected to take risks and taking those risks get officers killed. So eventually, officers may start to burn out due to constant stress, disillusionment, and apathy. They "burn out" and become jaded and short fused. They live with a "revolving door" criminal justice system and "cafeteria style justice" that lets repeat offenders off with little or no punishment and deterrent effect. They see the same criminals committing the same crimes, day after day and getting arrested by the same officer, who is taunted and mocked for being an Opie Pecker-head, Howdy Doody looking Mother F'er, and the usual variety of familiar colorful adjectives.
Cops are human and they get tired of the abuse and mistreatment too. They are commonly subjected to phony citizen complaints, (Mamma, he called me the N word!), and if you work in an inner city community, you will probably hear "300 years of slavery" every time you make an arrest. After years of a failed, liberal justice system, so many officers react by resorting to "street justice" - "You might beat the time, but you won't beat the ride" they develop an Us vs Them mentality, and they withdraw, feeling isolated and alone, backed into a corner.
Then the burn out starts.
When cops burn out they sometimes enter a spiral of excessive force, a little here, a little there, until it becomes a routine. The adrenaline is always amped up, shootings and questionable arrests happen, planted evidence issues, citizen complaints increase, prosecutions are thrown out and on and on. By that time a cop may be drinking too much to relieve stress until that becomes the norm. Then, domestic issues, divorce and further isolation. He usually only has other cops for friends. He is stereotyped, disliked and distrusted by the community. He will be told: "If you wanted to be loved, you should have joined the fire department"
Cops over react and act too soon sometimes because they are in a state of constant stress and a "Pavlov response" can turn out deadly in a confrontation between a citizen and police. Such as the previous case in Minnesota where the officer shot and killed an apparent legally armed black man on a traffic stop (in front of his wife) The victim supposedly made an inadvertent move, not with aggressive intent, and the officer reacted. This kind of stuff is going to happen but it shouldn't. I don't know for sure; I don't think that officer was a "bad cop" but he probably wasn't suited for the job. There are a lot of cops out there that are not suited for the job anymore, IMO (if they ever were) Not necessarily because they are evil racists, but because of a variety of other things such as inability to over come fear and the stress of the job.
I didn't respond to this post expecting that anyone would start being empathetic toward police, it's probably too soon for that, but most citizens aren't aware of, and don't take into consideration the specific cause and effects, human costs, and occupational demands of being a police officer. In the 60's and 70's minority officers in all of the under served communities was one of our important goals and we got there to an appreciable degree. It was a start.
I believe when changes and reforms come about, it will not be just because of the societal pressures against the justice system from without that we are now seeing, it will also be because young idealistic world changers, some of whom are now considered radicals, will finally figure out that change has to come from within. Just as we did, back in the 60's and 70's. And I don't mean political or revolutionary change as much as I mean evolutionary change, although politics may play an adversarial role. But don't be fooled, the power structure understands force most of all. If you beat your head against a brick wall you accomplish nothing. You have the key and the path to effect positive change, IMO. It's through the front door.