I've always hated the phrase 'ACAB', and I say this as someone whose username is Emma Goldman.
It's the institution, and its functional role in society, that's the structural problem. There are many well-intentioned, conscientious individuals in the police force. It is somewhat similar to the question of the attribution of moral blame for unjust wars. It is almost universally recognized that unjust wars are the fault of the aggressor country's leadership, and not the fault of the soldiers who fight them. Those soldiers tend to be poor, subject to indoctrination, and are often simply trying to dutifully help their country. In the same way that I don't think we should try and prosecute every Russian soldier fighting in Ukraine, or every American soldier to fight in Iraq, as war criminals - except for where they violate jus in bello - I don't think we should charge all police with responsibility for the injustices of the institution for which they work. Going back to where I began, Emma Goldman, one of the things I always found most powerful in the anarchist tradition is their belief in the basic goodness of most ordinary people - even when they are caught up in a fundamentally obscene system. I think I find the phrase ACAB grating for precisely that reason.
It's basically a simplification for life for some people. A lot of people don't like to think in nuances. Cops have a dangerous job and now that a large portion of the general citizenry hate them they have even more reason to be jumpy and sometimes aggressive. I think politicians could help a lot by ending programs like civil asset forfeiture, militarization of the police, etc. There is big gap between militant cops in small towns beating heads and what seems to be letting criminals do whatever they like in San Francisco downtown and then the DA letting them go because they did something less than shooting someone. I, for one, choose to live in a place with relatively stable "small town" cops even though they have sort of a bad rap in the neighboring city because they actually do patrol. I'm a brown person who has had zero problems with cops even though I have a lead foot.
> There are many well-intentioned, conscientious individuals in the police force
That's the issue though, I don't think this is true. Everything I've experienced personally and heard from others has shown me that cops will either 1) treat people like human punching bags or 2) stand by and laugh (or politely look away). Every single account I've seen from cops who've tried to stand up against police brutality has ended with that cop being retaliated against by their peers and fired.
If your premise were correct, then I agree that the slogan would be inappropriate. But I think the reality is that the police, as an institution, are extremely good at either excluding or converting otherwise well-intentioned, conscientious individuals.
It's the institution, and its functional role in society, that's the structural problem. There are many well-intentioned, conscientious individuals in the police force. It is somewhat similar to the question of the attribution of moral blame for unjust wars. It is almost universally recognized that unjust wars are the fault of the aggressor country's leadership, and not the fault of the soldiers who fight them. Those soldiers tend to be poor, subject to indoctrination, and are often simply trying to dutifully help their country. In the same way that I don't think we should try and prosecute every Russian soldier fighting in Ukraine, or every American soldier to fight in Iraq, as war criminals - except for where they violate jus in bello - I don't think we should charge all police with responsibility for the injustices of the institution for which they work. Going back to where I began, Emma Goldman, one of the things I always found most powerful in the anarchist tradition is their belief in the basic goodness of most ordinary people - even when they are caught up in a fundamentally obscene system. I think I find the phrase ACAB grating for precisely that reason.