crime and punishment
The majority of crimes are committed by a minority of people. Most people
commit no crimes. A person who commits one crime probably has committed or
will commit other crimes.
Therefore, if some crimes are unpunished, but other crimes are punished more
severely, then the average result is the same.
For example, suppose a person commits ten robberies. The government could
investigate and prosecute all ten robberies, and sentence the thief to five
years in prison for each robbery. The total sentence would be fifty years.
Or the government could investigate and prosecute only one of the robberies,
ignoring the other robberies, and sentence the thief to fifty years in
prison. The total sentence is the same, but the government saved money by
not investigating or prosecuting the other nine robberies.