Well, who votes for politicians? The public. Are all members of the public therefore culpable?

Voting isn’t a means by which every voter’s preferences are amalgamated into a coherent set of preferences.

Voting is better than the available alternatives, but one person voting for something better doesn’t make the outcome of the vote be that better thing.

You might have a point if we actually had an anti-police-corruption movement led by police officers - but we don't. The people who are supposed to be protecting us and enforcing the laws are really just bullies who like to abuse people, or they'd do something about it. They keep voting for union leaders who will cover up their crimes.