What's your reasoning for ACAB?
Usually, the argument goes something like: cops are selected for and trained to default on violence to control (most) situations they encounter, and are given license to use it in excess. If you passed that selection process and went through the training, you have shown yourself willing to default to violence. Hence, bastard.
But PP is describing the police doing what they are supposed to be doing, i.e. protecting people. If they were doing that, they wouldn't be using the excessive violence I just described, therefore no ACAB?