I have a theory that you can classify a criminal across two spectrums, and depending on where they end up on this chart would tell you a lot about how they should be handled by the penal system. One spectrum represents how likely an individual is to re-offend if they are released to society, and the other spectrum represents how serious the consequences will be if and when this person commits another crime.
As you can probably imagine, the serial rapist or child molester would probably end up being considered fairly high to re-offend and the consequence for their re-offence are also fairly high; this is primarily because their crimes are driven more by an uncontrollable compulsion that drives them to do some of the most vile acts we know of in society. In contrast, the University student with no criminal record who got into a fight with another drunk idiot at a bar over a girl he didn't (really) know is actually a fairly low risk to re-offend, and even if he does the consequences are fairly minimal.
When you are dealing with someone who you know will re-offend and will commit the worst offences longer prison sentences really do stop crime and make society a much safer place. In contrast, when you are dealing with someone who has almost no chance of re-offending and the crime they commit has almost no consequences then longer prison terms only make your prisons overflow.
Now, one thing most countries should embrace that would (potentially) reduce a lot of crime would be to give any criminals (where drug use was a major factor in their crimes) a sentence to a 6 month or 1 year rehab facility, and if they are a first time offender who has committed very minor crimes an "Automatic" pardon if they complete their treatment and stay clean and sober for 12 months after leaving the treatment facility. The hope of this would be that the number of drug addicts who use crime to pay for their addiction would decrease over time, crime rates would reduce, and the costs associated with running the treatment facility would easily be covered by the reduction in the cost of running prisons.
