The example is deliberately contrived and hyperbolic. In real life, if there is reliable evidence that someone is murdering people, the police conduct an investigation, we have a trial, and they go to jail. You know what we don't do? We don't go "Hey, I think Bob the pen-seller is a murderer. Nobody buy his pens so hopefully he runs out of money and can't afford to murder people anymore". We don't do that because it would be a really stupid and ineffective way of stopping murderers, and it's really stupid and ineffective for most other things too.