My experience is obviously atypical though. I saw many people mentally deteriorate, attempt suicide, and essentially give up hope in life while under this sanction. What is worse, the state at that time was imposing a truly inhumane punishment on the rastafarian community within prisons. Due to the rastas not following prison grooming habits by refusing to shave off their dreadlocks, the prison system moved a group of them into the hole. When I left it, some had been there for 10 years straight. I can assure you that many of these men were deeply disturbed.
I was lucky in that I have a psychology that can endure this sort of abuse and come out of it stronger, but most people are not wired like this. Given what I have seen, this really is tantamount to torture. I wish so much that normal US citizens would tour a prison and see what this does to people, because maybe then this would be outlawed.