There are a lot of problems with how solitary is used in the US prison system. There are a lot of problems with the US prison system in general. But to call solitary ‘torture’ is to cheapen the word ‘torture’ and to begin a path of eliminating its usefulness as a word to describe acts that should not be committed ever.
There are (a very few) cases where solitary confinement has a legitimate, short-term use. Cases that should be very, very carefully considered before it’s employed. There are no cases where torture is justified, for any reason. I feel that it’s important to retain that distinction.