Is this true? As far as I know the penal system has one and only one purpose: deterrence. 1) and 2) are a practically-oriented bonus. 3) is, to my knowledge, explicitly not a goal.
> The court, in determining the particular sentence to be imposed, shall consider ...
> (2) the need for the sentence imposed—
> (A) to reflect the seriousness of the offense, to promote respect for the law, and to provide just punishment for the offense;
> (B) to afford adequate deterrence to criminal conduct;
> (C) to protect the public from further crimes of the defendant; and
> (D) to provide the defendant with needed educational or vocational training, medical care, or other correctional treatment in the most effective manner;
"recognizing that imprisonment is not an appropriate means of promoting correction and rehabilitation."
In contrast, serving sentence in prison may change their personality.
So as I see it: it's revenge + lesson to people outside, to not commit crime.
I'm not endorsing this practice, just stating how I think deterrence is alleged to work.
I think that is the innocent opinion.
If it were for deterrence, then it would need to effectively deter better than it does. It does deter some people, but perhaps not others (especially in the US with its extremely high incarceration rate). And do life sentences effectively deter? It is possible to measure deterrence scientifically, because there is variation.
Also for it to properly deter, many of us would need to experience it first. From the outside we “know” it is horrible, but experiencing it is the only way to bellyfeel just how horrible. And what about the people who like the scene, the routine, and zero responsibilities?
How many people must be deterred it a balancing act. If jaywalking is punished by death, it will deter most people, but it is not adequate to the crime. And even death is not enough to deter absolutely everyone. One has to find the right balance.
Experiencing it first hand is not needed at all in my opinion. Per the above, it just has to work "well enough", and it usually does, even in the US.