It depends on the length of isolation. As a young man I spent many months on lock up (jail slang for solitary). While I agree the US has become a police state and we incarcerate far far too many under increasingly draconian laws we have to ask under what circumstance these people are being isolated. For me personally it was because I was extremely violent and impulsive. I had little choice because of my age and the environment, but I also left the administration little choice in how best to protect the correctional officers and other inmates.