Actually the last is a clear misapprehension. Let's start with the first part you mentioned though, that all cops are human. Let's look at the consequences of that...
I start with actual systemic issues...
1. Like any human system, the larger the system (police force in this case) the harder it is to select/weed out the incompetent, if you notice the vast majority of issues actually come from the larger sized police Departments, hundreds if not thousands of officers.
2. Human systems also often suffer from corruption created by nepotism, patronage etc., Essentially top down corruption. This used to be a HUGE problem in Police departments, especially large ones. In order to try and eliminate that issue Civil Service Systems were created. The problem there is that it is a two edged sword. It helped mitigate the top down corruption BUT it creates a series of procedural hurdles to discipline which the incompetent/corrupt officer can exploit. Then you add in Federal Labor Laws which make the release of certain actions against employees Civily Liable and you may never know that the PD actually did address the issue at earlier points in a particular officer's career. This last part I think is important. In erms of labor protections of any employee and then add in additional protection from civil service rules that were created to address political corruption and then, in some cases, protections created by collective bargaining agreements and you have an issue that is not so much a "police officer" issue but one that can only be resolved by statute.
3. Incompetence, is not always incompetence per se, it can be a training/hiring issue. The public essentially wants high levels of protection for rock bottom prices. A simple example, last week I did my annual firearms qualification. Not only is this the only time the PD will have me shoot my weapon on "company time" for the entire year, it also is done on duty time so as not to cost OT. Thing is that during that time the street was short multiple officers, creating higher stress and thus greater chances for mistakes of those officers covering the town for the 5 hours we were out of service. We would not have been able to effectively respond to an emergency because the range is 30 minutes from town.
Because of this lack of training you can tell who shoots on their own time. I scored a 296 out of 300, I have seen other officers have to qualify twice just to get the minimum score (240).
4. A misunderstanding of the law. I am not talking about her people who don't actually understand how the 4th amendment works, that I can detain you and have it legally not constitute a siezure, rather the difference between Criminal and Civil Liability and actual standards for the use of force.
A. For liability there can be times when an officer violated a procedure that results in a bad out come BUT that violation of policy doesn't constitute a crime. You sue them.
B. Use of force. The use of force is determined by using a legal construct of whether the use of force as seen as objectively reasonable given what the officer knew AT THE TIME and without the use of 20/20 hind sight. So maybe afterwards they find out the gun was a novelty lighter or a BB gun... Their shooting was still legally justifiable.
What does all the above amount to? The system I'm bears the most responsibility. Police are one of the most visible symbols of the system. People often think that you can't "fight the system", so they instinctively make the Police the goat for the system's short comings.
The individual officer element.
1. I will be the first to admit that if an officer does not personally know if the officer is good or bad they may well initially defend an officer, barring compelling evidence. Few ever ask "why" though. It's not different than any other community. How often do we see people reflexively defending a member of their circle (family, community, etc), especially if there is an "us against them" attitude, whether that attitude is justified or not?
The "us against them" dynamic is as much a part of LE culture as any other. There are a great many circumstances where Officers were relexively accused of wrong doing based on some edited or editorialized video and then it turns out the officers were actually in the right. As an example I remember a YouTube video where someone was narrating a video of an officer involved shooting saying "look they just threw a drop gun, look another what the hell!!!" Thing is they were actually flapping as they fell, guns don't flap. What were they? Nitrile gloves that the officer who pulled the trigger was struggling to put on to render first aid. He was still dealing with the adrenaline and after shock of pulling the trigger and was shaking so bad he couldn't get the gloves on. Then you have cases like this as well...
Yet all too often if the evidence does clear the officers the people who raged over a viral video never know this is the case. They continue thinking it was unjustified because media coverage like the one in the video is fairly rare since the media has moved onto the next click bait headline. For months, even years later they keep hearing a case that was truly justifiable raised as a rallying cry for injustice. What effect do you think this has?
Rushes to judgement based on limited information and then that false judgement persisting regardless of the facts feeds an "us vs them" mentality. Is this mentality "right"? Of course it isn't, but if people would actually wait until everything investigated before marching, calling for arrests etc. Officers would be less apt to jump instinctively to the defense of another officer because they would not be able to point to the numerous rushes to judgement as a justification that certain segments of the population are "out to get them."
Again none of this is to say there are not incompetent, even out right racist and corrupt LEOs. In the end though I think society needs to consider what this article explains better than I ever could if you really want police reform...
Is America ready for the true cost of police reform?
What everyone wants, even LEOs, to have happen is going to cost money. How many Americans though do you think would say "sure" to their taxes being raised to pay for it.