Then you, like many others, misunderstand what the saying All Cops Are Bastards means. It's not an observation about the morality of each individual cop. It's shorthand for the fundamental corruption and injustice inherent to the institution of policing itself.

If Mother Theresa or Mister Rogers becomes a cop, ACAB isn't suddenly disproved, because it's not about specific individuals and their specific moral qualities. It's about systemic and fundamental problems with policing as a whole.