So many Americans are either in prison or jail that the effectiveness of a jail term is diminished by the amount of actual time served. If people serve only a fourth of their sentence because the jails are overcrowded, they don't learn anything. Corrections officials need to increase the speed with which capital punishment is enforced and find other, more effective methods of punishment.
The United States of America would do better to put more people in prison. Economically, there is a large cost to keep people in prison. This is the major argument for less people in prison. I would counter that the cost of not incarcerating them would be more. If you think about all the fraud, theft, burglary, and vandalism that they would be committing while free starts to add up. Then consider all of the food stamps, welfare, and housing subsidies that they take. Summing all of that up would be more than the cost of keeping them in prison. These people are not redeemable.