It's very difficult to calculate the sum of externalities introduced by long-term imprisonment. Crimes will be reduced at the public level as could _potentially_ be engaged in by the convicted, however:
1) The criminal is free to commit crimes against others in prison, which may further criminality in those individuals when they are released.
2) There is a burden on families, especially children of those incarcerated. The fostering system seems to result in a lot of future criminals.
3) The economic cost of a 20 year incarceration is probably about $50-100k per annum per prisoner in most first world countries. It's possible that this money being spent on programs to enable to impoverished to escape poverty or investment into programs or drugs to treat criminals would result in greater net reductions in crime to the public as compared to incarcerating a single individual.
1) The criminal is free to commit crimes against others in prison, which may further criminality in those individuals when they are released.
2) There is a burden on families, especially children of those incarcerated. The fostering system seems to result in a lot of future criminals.
3) The economic cost of a 20 year incarceration is probably about $50-100k per annum per prisoner in most first world countries. It's possible that this money being spent on programs to enable to impoverished to escape poverty or investment into programs or drugs to treat criminals would result in greater net reductions in crime to the public as compared to incarcerating a single individual.