Every organization needs rules. Otherwise, it isn't particularly organized, is it? And it's reasonable to say that members of the organization should have a say in the rules – not necessarily a huge say, but their voices should be heard. If they don't like the decision, they can always e.g. join a different church. In the extreme, every voluntary organization can be exited, even if it is dear to us.
Exit isn't always our choice. Any group that can't eject harmful members will always be plagued by bad actors. Fandoms can't, so they are known by their most pathetic elements. Most organizations have entry requirements and their exit procedure is so mild it never even occurs to you to worry about it – The Rotary Club surely has this capability, but I've never even heard of them using it, and surely they use it sparingly.
But there's a difference between not ejecting people unless you have a very good reason, and not ejecting people. I was once part of a local meetup that almost fell apart because one of the members, thinking he was just stealing the tip off the table of the restaurant we met at, was actually stealing some people's payments. We almost got barred, eventually had to move to a much worse meeting place that was less convenient for some, and the lack of being able to eject this person almost made the cycle repeat.
Aside from being dreadfully embarrassing, it almost destroyed the group. And that was just one person!
So when a police officer gets fired for giving a homeless man a shit sandwich, that's the system working properly. When he gets reinstated and enough back pay to make it just a multi-year paid vacation, that should raise eyebrows. Frankly, that case is more marginal than the typical police officer misconduct case, and we should be ashamed of using it as a totem. There are plenty of police shootings that, if a security guard were in the same situation, would be called murder. In those cases, the police officer found to use force inappropriately doesn't get charged – but in fact gets a paid vacation while being investigated and almost certainly not fired.
Police unions do not want the strongest police forces – their role is to stop any ejection of personel. This makes the police weaker, more incompetent, more vicious, more stupid, and more prone to expensive liability lawsuits – any reason you might fire a cop to make the force better won't work (because almost all firings are stopped). The only time when they'll let a police officer get fired is... actually, read this piece yourself. It's quite good.
I am not the only human that thinks lack of discipline is bad for law enforcement. It is as close to a fact as you can pull out of the social sciences. Police officers have rules for use of force that don't meet the military standards for use of force, and those are for wartime.
I can't overemphasize the Onion-level hilarity of the Reason article. Here it is again. The next time you think a public sector union serves both their members and the public, I'd take at least four attempts to see how that might not be the case. With any fewer, you might not see the system in all its strange complexity.