Why?
Why is the self appointed leader of the free world so inhumane?
For prison to work as a disincentive, people need to be capable of making sensible decisions about what to do NOW in order to create a better distant future. They often aren't. Criminals are often people who do very badly at this. They don't want to be in prison twenty years from now, but it's not going to affect how they live their life now.
If prisons as thought of as primarily a disincentive, it's a very expensive way of getting not much back. I expect it's a cultural thing.
Yes there are cheaper and more effective disincentives, but you're right it is a cultural thing. Our culture considers those barbaric (but not prison somehow.)
It's very difficult. We can look at the fact that the US imprisons more of its population than any other nation, and if prison is a working deterrent, this would mean that the United States is a phenomenally lawless and criminal society barely held in check by the fear of the USA's notoriously harsh judicial system. Is the USA a phenomenally lawless and criminal society?
There are studies that try to evaluate the deterrence effect of prison. Some conclude yes, some no, but the weight of evidence appears to indicates that on the whole, it's a pretty ineffective deterrent. You can google as well as I can so I won't list a bunch of google hits.
"Our culture considers those barbaric (but not prison somehow.)"
Now that is interesting. I meant a detention system that actually works; that actually is applied with the intention of turning criminals into good citizens and making a better society. I assume that you don't consider that "barbaric", so I'm guessing you thought I meant something like state-sanctioned torture or other such physical abuse, or cutting off people's hands, or public executions in the town square, and all that sort of thing. So our cultural gap is so big that the first thing you thought of to deal with detention as an ineffective deterrent wasn't an effective detention system, but harsher punishments, whereas I thought of stopping trying to use it as a deterrent and do something useful with it.
How else would you explain the widespread of tobacco smoking, over-eating, and other behaviors that are extremely dangerous but not immediately punishing?
One of the highest prison populations in the world. If it were a deterrent, people wouldn't commit crimes that get them in prison, would they?
Either its no deterrent, or Americans are the most criminal in the world.
We might have more crime than other first world countries in general, but it's not like prisons are the cause of it. That doesn't mean it doesn't work.
Besides, what are you comparing it to? All other countries use prisons as well, and what would the alternative be anyways?
If you want either to work as a disincentive, you first must make people be in control of whether they enter that next state of hell. This article clearly shows that prisoners aren't; they can just get sent to solitary (for decades!) because the wardens don't like them or find them a nuisance.
IMO, especially in the USA, many people aren't really in control w.r.t. the "do I want to go to prison?" question either. If you happen to be born in a poor neighborhood, you have to be exceptionally strong mentally not to get involved with petty crimes such as marihuana dealing, and if you do, you can get locked up. When you get out, you return to that poor neighborhood, and, having a record, you are certain that you cannot get a job anymore.
I still have sympathy for (most) people that commit crimes, and I think it'd be inhuman not to. That's why we don't have the death penalty for all crimes, regardless how effective a deterrent that would be.
On the other hand, if you know the consequence of committing a crime and decide to commit it anyways, I don't have as much sympathy. You can't say that people have no choice whatsoever. Just because you grew up in a poor neighborhood doesn't make committing crimes ok.