The phrase acab does not imply that literally every single police officer out there is corrupt, a bad cop, whatever, but rather that the police as an institution in general corrupt to the core, acts on impulse, aggression, racism. The goal is to point to the wrongdoings of the police as a whole, as a system.

It's the same thing when people say that, as a whole, all men are pigs or something similar. Yes, of course there are men that aren't but the vast majority of them is. The phrase is pointing to patriarchy, rich white men ruling the world, essentially, toxic masculinity and many other things.

vegan btw