Do you know why ACAB? Is not because they are rude, it's not cause they mean. It's because they participate in a societal role that requires them to do bastardly things.
They have to enforce unjust laws and unjust outcomes, and statistically do so more heavily across minority populations.
The institution requires them to be bastards, ACAB is a statement about the institution of police and the people who elect to join that institution.