As usual, a thinking disconnect is responsible for the hoier-than-thou conclusion.
Putting any one or any ten offenders in prison is not supposed to reduce the crime rate. It may. It may not. It might be the case that the police catch the easiest to catch criminals who commit fewer crimes “each”.
The purpose of putting a criminal in prison is to prevent that criminal from committing more crimes and to protect the property and safety of the people who are already committed to financing the facility, the prison, where the criminal is to be housed. And that is or should be the start and end of the story.
As the number of criminals in prison increased, the crime rate dropped.
When criminals are in prison, they are not committing crimes (at least against people outside of the prison).
Hard to believe that the author disputes this. The numbers are clear.