This isn't politics, it is feelings. The word black is a label, which has a history of being used as a racist term. So it is understandable that there may be some ill will about it. Understandable, but not necessarily warranted.

Now the word "cop" is a label we associate with a job, it has been around for decades, it isn't derogative (unless you as a police officer are offended by it). What we have here, is people being offended by what has happened, not by the adjective of the job.