for every story of heroics there are 10^n times as many of bad experiences ranging from petty issues to brutality. police do not only not serve and protect, they frequently actively harm the communities they patrol
anecdotal counter-evidence will not be taken as a valid argument, either - just because you know cops that haven't either harmed you or claim to not have harmed anyone unjustly doesn't make policing as a whole less morally reprehensible