All Muslims are represented by the worst of the Muslims. All black people are represented by the worst of the black people. Therefore it would be in their interest to weed out their own worst members.
Come on.
Come on.
Noone can force you to leave the Muslim or the black population; you are what you are, and so any suggestion that someone should be removed from that population is pointless (unless, of course, one thinks murder is an acceptable method; I am not suggesting that you do)
The police (or engineers; nurses; judges; etc) are a professional body; it is in their best interest that certain minimum standards apply to all members, thus making the public trust the competence of any representative.
It's not the fact that there are bad apples people are angry about (we understand there are bad apples in every profession). It's the absolute lack of accountability that is the issue.