I have a question

I want to preface this by saying that I’m not trying to argue with people, I just want to see both sides of the story. To my understanding, ACAB arose around the same time as BLM, and what those officers did was horrible. I’m not defending them or any other discriminatory officers. But to my knowledge must police are actually trying to do the right thing. So isn’t saying that all cops are bastards discrimination in and of itself? I just don’t fully understand the ACAB perspective, but if there’s any crucial info I’m missing, please tell me.