It's not a problem of policeman brutally beating/killing people (its a issue alright but). Its about the organisation protecting and turning blind eye on their misdeeds.
There will be bad apples in any organisation. Be it police fore or church. The problem starts when the perpetrators are protected insted of being ousted.
That emboldens other to do similar and openly advertises to anyone 'Join our org and you can to X, Y, Z with no repercussions'.