Ideally the police should come out every single time, and the discretion of when they should be called in the first place should lie with the community.
It's when people get lazy and/or paranoid, then turn to the better-safe-then-sorry model, in addition to the police meeting budget and manpower requirements that they must arbitrarily enforce a threshold for when they should actually act.
It's tough.. but.... :/
edit: regarding the "taking things into your own hands" part... I had a little chuckle (from remembering the little "tolerance" talk with Ark above).