"Police officer" or "cop" are words used to describe people who commit specific acts. Just like "rapist", "child molester", or "mugger" are words to describe people who commit specific acts. It's not really about the person, but about the acts the person chooses to commit.
Objecting to those acts being committed or to those who commit them isn't at all similar to racism or sexism, because it is based only on actions and the individual person who commits them. Nothing else.
To say "not all police officers are bad" is a nonsense statement. You are denying the description and the definition.
Let's say, for the sake of argument, that "sheep" is defined as "a white, hoofed mammal with wool". In that case, a black sheep wouldn't fit the definition of "sheep"; you'd need to make up a new word to use for it. And, a tuna clearly wouldn't be a sheep.
Well, a "cop"/"police officer" is a person who enforces laws-- both the unnecessary and the harmful-- and violates property rights while claiming to be protecting them, with violence or threats of violence, on behalf of a government. That isn't a good person, by definition.
To pretend there is something you would call a "cop"/"police officer" who doesn't do the above is to describe someone who doesn't fit the definition of a cop or police officer. You are talking about a completely different set of acts the person commits-- as in the case of a free market "police" analog. You are calling a bald, black unicorn a sheep.