Solitary confinement is psychological and physical torture. Men who haven't even violated any prison rules are forced to live alone — to the point of hallucinating and suffering post-traumatic stress syndrome — simply because they have gang tattoos. The inmates on strike aren't even asking for much, only that they be given access to human connection and fresh air so long as they don't break any rules.
Solitary confinement for known gang members isn't an arbitrary prejudicial practice, it's a preventative one. Prison authorities know exactly what happens when you put adversarial gang members in the same general population, and it's dangerous. While solitary confinement is sometimes characterized as "torture," it's actually safer for both the inmate and the facility staff.