I'll explain for you in case you're not trolling. We must All Cops Are Bastards because enough of them are and there is little enough oversight that when some of them do something wrong they get away with it far too often. It is therefore self defence to never trust a cop because they can fuck your life up six ways to Sunday and suffer no repercussions of note. ACAB does not mean there are no good cops, it means we must assume any given cop is a bad cop because one false negative has the potential to go so far wrong.
Your even spicier take is actually just bonkers. It's not a uniquely US thing, no, but it is not designed to do anything but protect us the non-cops!