This argument confuses stopping crime with deterring crime. The police’s job isn’t so much to arrest people, as to arrest the people they have to in order to make an example of them for the community. This reduces crime by preventing it rather than stopping it. In fact, making more arrests publicly for petty offenses does not reduce crime. Therefore, the police do not arrest people and stop crime – they merely arrest people
. If arresting more people stopped crime, then more stop-and-frisk arrests would result in fewer people arrested because fewer people would be committing crimes. This is (statistically speaking) not the case. Arrest rates have no effect on violent crime rates
. Therefore, the police may stop crime and arrest people, but their real job is to deter more crime by doing this.