There are people in prison having a far worse time than Manning. Come to think of it, if I were in prison I'd much rather be in solitary confinement like Manning than in with the general prison population (where my options would presumably be either to join the Aryan Brotherhood or get beaten up every day).
A lot of people have tried solitary confinement for the reasons you bring up, but more than a couple of days of it and most of them decide it's worth taking the risk in the general population. Solitary confinement is a weird experience.
He's in a military prison , not Riker's Island.
How do prisons become HN-worthy content just because someone involved with internet drama just happens to be in the prison?