Even though prison is neither very good at keeping criminals separated from society, nor very good at deterrence, the main purpose is still keeping criminals separated from society.
Prison also deters different criminals by a similar consistent amount, since it reduces their utility. Corporal punishment does not reduce utility much but inflicts a subjective amount of pain, which some people might consider traumatizing, while other people might consider a cool "rite of passage" which demonstrates their toughness.
Nonetheless I agree with your observation that people place undue weight on the "unusual" part of "cruel and unusual punishment," and seem to be perfectly okay with prison and all the shenanigans which go on in prison, while completely shocked by any alternative idea.
It reminds me of how people are shocked by people abusing their pets, seeking to punish pet abusers as harshly as child abusers. Yet there they are eating meat out of a factory farm with 10 times worse animal abuse. Their sense of morality is governed by "if everyone does it, it's okay," yet at the same time they are shocked by societies in other places and times where what "everyone does" was different.
I’d rather see the prison system less barbaric than try to find ways of intentionally inflicting that level of barbarism in a compressed form.
Regardless, I think you still need confinement of some sort for people who are dangerous but not deserving of the death penalty.
Corporal vs jail is overdetermined - the former shocks and horrifies people, most people would also choose the former.
I would caution against torture. I can't articulate the reasoning, but I feel that torture is worse/ less wholesome (for both the torturer and tortured) than pain caused by straightforward damage.
It is also less scary - the idea of being tortured without any real damage isn't visceral the way beatings are
P.S. you should care about justice/vengeance, and in those areas I believe corporal punishment >> torture/prison
Preceded By: The case for the death penalty
Scott's essay https://www.astralcodexten.com/p/prison-and-crime-much-more-than-you is going to be my main source for most of my claims here, I recommend reading it either before or after.
Prison is very expensive, on the order of $100,000 per person per year. So what are we getting for our money?
I know of 4 main purposes of prison[1].
Unfortunately it's not really cost effective for any of them.
In those situations where it's worth paying extremely high costs to prevent someone even being able to commit a crime, my preferred solution is to execute them.
But how do we cheaply and effectively deter thieves, in a way that shows police their work is effective, and doesn't throw a wrench in criminal's lives that might force them down the wrong path?
The answer is obvious. Instead of locking a criminal up, thereby causing them a small rate of pain/unpleasantness over a long period of time, find something that causes a similar total amount of pain and unpleasantness but compressed into a much smaller length of time.
The biblically mandated solution is 40 lashes, and I think that's definitely in the right direction. Unfortunately severe beatings can cause permanent injury and high medical costs. However the intelligence services of the world have invested lots of effort into researching useful questions like how do you cause the maximum psychological terror to someone whilst minimising physical harm. They may be able to provide some useful advice.
For any length of prison there is a level of torture where someone would be indifferent between the two options. Switching a prison sentence to an equivalent level of torture would be no crueller to the convict, would be far cheaper to the state, scales far better than prison, would presumably have only limited difference in deterrence, and would allow the convict to carry on with their life as normal afterwards.
Plus it would show police that petty crime is taken seriously, and catching criminals isn't pointless.
Objections
But torture is barbaric!
Of course it is! And so is prison! The difference is that people in prison are locked behind iron walls where you don't need to think about them, and that prison is a minor barbarism played out over a long time, instead of a major barbarism played out over a short time, thus far easier to ignore. It doesn't make much difference to the convict either way.
But the constitution forbids cruel and unusual punishment!
Indeed it does! And when it was written corporal punishment was the standard, and imprisonment was unusual. It is far more likely that the authors of the 8th amendment would have considered imprisonment cruel and unusual than a beating.
But torture causes long term physical and psychological damage!
Indeed it can! And so does prison! But whereas changing the prison system to remove negative aftereffects is difficult and expensive, with slow feedback loops, adjusting torture to minimise aftereffects can be rapidly iterated on and cheaply implemented.
Ignoring vengeance and justice, which don't interest me.
Or at least till they're old enough they're not much of a threat. But at that point they have poor health, they don't have a pension, and they don't have a job, so the public is still going to end up footing the bill for their food, rent and healthcare.