I think the failure of the phrase ACAB is that it pins the problems of the system just on cops. Corrupt lawmakers, judges, district attorneys, prosecutors, and defenders all play into this as well. Lawmakers made the laws defer to cops over citizens, judges treat a cops word as more truthful than a citizens, same with district attorneys and prosecuting attorneys. They’re all scratching each others back in a sick system where nearly all of them are essentially above the law.