This is not a question of about parroted nonsense and cultural norms. I mean what end product do they produce that justifies their existence in the first place.
I’m physically disabled and have been living in a prison like situation for nearly 11 years. How does my situation balance into the ethics of prisons? I’m on a path to homelessness and a premature death due to institutionalized neglect and abuse from US institutions. Criminals are housed and fed in exchange for similar isolation, abuse, danger, insurmountable debt, and a largely unemployable and destitute future. These seem to conflict in ethics.
Since I’m not a psychologist or even (alas) particularly empathetic, I will leave aside the fact that this post appears to be a veiled cry for help, and answer the actual question.
Prison exists to protect society from dangerous individuals, but also because it’s the simplest form of non-corporal punishment. Flogging and flaying and chopping and mutilating and so on are all well and good but at some point in humanity’s march to civilization such things will start making the rulers queasy and it becomes more palatable to just lock the problem up for a while.
Personally I have a radically liberal take on this. I think that the purpose of punishment (other than protection, as mentioned) should be not retribution but rather restoration. In my ideal world, prison sentences would mostly be swapped for various forms of community service.