... when this is what we allow?*
Society is judged not by how the fortunate is treated but by our actions towards the less fortunate. The number of people we incarcerate every year is appalling by itself but how they're treated is a disgrace to this country. But they're criminals, you say, they committed crimes, they deserve to be treated this way. If they wanted to be a part of society, they shouldn't have broken the law.
If you have broken a law in this county, in many prisons, you can expect to be raped or sexually assaulted by inmates or guards. You may be put in solitary confinement for weeks, months or even years. If you have health issues, they could be ignored until it's too late for effective treatment and mental health issues will be almost certainly ignored.
The point of incarceration, whether punishment or rehabilitation, is a good question but regardless of the answer, under no circumstances should a country treat any of it's citizens (or visitors to this country) this way. It goes against everything a moral, civilized country should stand for.
*America's private prison system is a national disgrace