The point of "police are not your friends", is you can't know which cop has a chip on their shoulder until its too late and you're three teeth short of a smile. The nature of policing and the logic behind "ACAB" is that because police don't keep their peers in line, you cannot trust any cop.

"One bad apple" has been corrupted just like "Pick yourself up by your bootstraps". The former cuts off "spoils the bunch", the latter being a satire for something obviously impossible.