Rehab in the American justice system is a better way to get to the root cause of a person's crime rather than punishing certain offenders for their bad ways. Some criminals should be locked away and kept out of society. However, most of them should at least have an attempt at rehabilitative services before rejoining regular society. Rehab, in the long term, will keep jails from getting overcrowded with repeat offenders. More people in the workforce means more taxes are paid and more consumers spend more money. Fewer people in jail mean less taxpayer money is spent to house criminals for long terms.
Ideally, rehabilitation is better all the way around. There is no question it is a better deal for the offender. Instead of being punished the offender gets a new chance and new hope for life. The offender gets free medical treatment and avoids the punishment he likely deserves. The only negative, which is a huge negative, is that rehabilitation rarely works.