The ACAB people have never been opposed to laws or prosecution of criminals. The problem is that the cops and their powerful friends tend to be immune to those laws.
It's certainly true that some laws and some sentencing ranges are unjust, but that's different from saying that laws themselves ought not exist. And although we've seen several high profile cases recently where prosecutors are clearly dirty as hell, that's probably less common than the dirtiness ratio among the pigs.
Also, ACAB doesn't mean there are no good cops. Just that even the good cops are sullied by being a part of an organization that promotes and protects those who commit terrible crimes. Sort of like, "Even the really good ones are sort of bad."
You're both saying pretty much the same thing. ACAB isn't really about the people, it's about the system that's set up to promote abuse of power and suppress those trying to do good. Cutting the rot won't solve the problem because there will always be more rot. What's needed is complete reform.
"A rotten apple quickly infects its neighbor", the 1130s version of the famous proverb.
It also suggests the solution: remove the bad apples before they can spoil the bunch. But, bad cops are protected, and as a result the whole institution is rotten.
Also, if you end up with a whole box full of rotten apples, the only solution is to throw it away and start fresh. Police reform processes almost never do that. They try to keep most of the cops, even the supervisors, in their jobs. Then try to fix it with extra training, or outside supervision or something.
There should be laws, and if there are laws there's a need for law enforcement. But, other countries around the world have managed to do that in a way where their law enforcers are properly supervised. They've found a way to have specialized units that deal with violent crime or organized crime, so that the rest of the law enforcers don't have to walk around with a life-or-death mindset. Most importantly, they have a culture that a police officer is a public servant whose main job is to help people in very stressful situations. In the US the culture is that every person you encounter is potentially going to kill you, so you and your brothers need to approach every situation as though your life is on the line.
Good cops don't let bad cops do bad things. Which is another way of saying that I agree with you, but I would prefer to categorize cops based on their actions and not based on their theoretical potential, because we have to live with the former. Or die from it, as happens all too often.
This is too broad an interpretation of ACAB. The concept is specifically about policing and takes no stance on the concept of law. That's a consideration seated in political theory. No movement is a monolith. Progressive liberals, socialists, and anarchists alike share ACAB in common but have differing views on laws/enforcement/justice system.
Prosecutors are like cops more than they are different. They work with them day to day. They have the power to charge the bad ones with crimes, but they rarely do, and even then they often overcharge or put up a poor case so the cop goes free. They also overcharge people to force plea deals and avoid trials. This goes double for those who can't afford bail and have to spend years in jail waiting for a trial. Prosecutors are every bit as bad and corrupt as the police.