It's a changed world from when I worked. Keep in mind as society changes, so does the pool of police applicants. I had a chief say many years ago he could not keep standards and fill an academy class. IMO, there has been a significant societal/moral decline during this time. Not to politicize it, but a key turning point IMO was when the president in the mid-90s was caught in decidedly immoral behavior, lied about it, and then was given a pass. If we cannot hold that person accountable, what lesson does it send to our kids? BTW, those kids then are all adults now. For equal time, elections during my lifetime have devolved into usually voting for the lesser of two evils, to include the current president- who nearly daily sets a poor example for our children in how he treats others. I heard a commentator say once that his goals are similar to those of President Reagan, but his way of attaining them are completely different. Contrast his pride with the self-depreciating humor of Ronald Reagan, and it is night and day. The last federal candidate I voted FOR is quoted in my signature (I still vote), and that was 8 years ago.
There is far less respect for police than when I worked. Some- fortunately very little- of it is deserved.
Police kill a black man, news event similar to a natural disaster- unless of course the officer was black. Meanwhile, thousands of black men kill other black men and read about the story on page 25 if at all. If you look at violent crime numbers, a hugely disproportionate amount is committed by blacks, usually against other blacks.
Where I live, that holds true. About a dozen mainly black men are killed by gunfire each year, and in each case the killer was another black man. The research I've done shows that in over 3/4 of the cases, an illegally-possessed gun (in violation of existing laws) was used, but no one seems to care about that. A couple of years ago, two white women were killed by a white man and it was national news. What's really sad IMO is how so many give lip service to what Dr. King said about judging by the content of character, not the color of skin. So long as we continue to use inaccurate terms such as African-American (which is not a race), we continue to divide not unite. We live in these United States, and E Pluribus Unum still means out of many, one. More lip service to many. Our republican Florida governor recently touted one of his court appointments as being the first Caribbean-American to hold such a position. I LOL'd. My question- what were her qualifications? I really don't care about where she was born or the color of her skin.
As with other things, the media coverage or lack of coverage fans the flames or places it into obscurity, and is used as a tool to further divide people. We live in a dumbed-down short-attention span society, where the term "real quick" is uttered daily. Younger (and some older) folks live on "social media", which focuses on self ("Look at ME!!!!!") not others. It was Democrat John Kennedy that said "Ask not what your country can do for you, ask what you can do for your country." He'd be unrecognizable to his party today.
Now on to your points-
1) The gore of auto wrecks in my case was not the bad part. The bad part was telling next of kin about the death, especially if it was a kid. IME, those in the profession long term either gravitate to a less-stressful position with better hours or become emotionally detached, sometimes both. Some turn to alcohol due to the stress. Constant exposure to stress changes people over time. This is not unique to police. Look at complaints against judges and you'll see the effect there as well. PTSD is of course well-documented for those that have served in the military, thanks in no small part to fighting in other people's endless wars.
2) The killing in Atlanta did NOT involve police. The father was a retired deputy. While I have not read extensively about that case, I did read the fellow that filmed it has now also been charged with murder. Seems like non-existant cause for murder.
3) Yes, it takes a lot of time for a proper criminal investigation, even with a lot of help (I mainly worked alone). You have to collect evidence, that evidence has to be processed (can take weeks if not months, it's NOT like CSI or any TV cops), witnesses have to be tracked down (a lot more time spent doing that) and interviewed. Interviews in some cases have to be transcribed. The report must be reviewed by a superior. It then goes to a prosecutor who may or may not want to file, despite there being sufficient probable cause.
4) Body cameras and things like collecting traffic stop data came about IMO since some in power believed we could no longer trust police. See my initial observation about societal/moral decline. There is a mindset in modern America that "If you have not done anything wrong, then you won't object / you have nothing to hide". That flips many principles found in our Constitution on their head. You cannot prove a negative. As with laws that punish innocent Americans (USA PATRIOT being a main villain), laws/policies/procedures often punish hard working honest police officers. One or two mess up and ALL are painted with the broad brush.
5) There is a way to report police misconduct. As with anything else (cars, appliances, guns ) it's easier to join a forum / go on "social media" (another cause of moral & intellectual decline IMO) and complain than to take the time to follow through. People like water & electricity follow the path of least resistance.