We already have laws concerning animal cruelty, and they are far more humane than the laws we have for human beings. That was the point. Human beings are supposed to be considered more important than animals, yet we have animal cruelty laws that are more humane than laws for human beings. And we recognize that a dog that killed someone doesn't have the capacity to think as a human being but will think like a dog and rightfully blame the dog's owner for the dog being dangerous and given the opportunity and desire to kill someone. Yet we DON'T believe that it's proper to punish the dog by confining it to a too-small cage without interaction with others for 23 hours a day for the rest of its life because we rightfully believe that a dog forced to live in those conditions is cruel regardless of what the dog did or how dangerous it may be to others.
That's the whole point. We recognize that treating a dangerous dog to solitary confinement 23 hours a day for the rest of its life is considered cruel but we don't consider that cruel to do to a human being. We also DO have many and large organizations dedicated to rehabilitating dangerous dogs so that they may be able to live freely again with a new and responsible owner, yet our prison system is designed to not attempt rehabilitation of human beings and usually makes prisoners even MORE criminally minded.
Ironically, we also believe that euthanizing an animal to end it's pain and misery from illness or old age is considered a kindness, yet we force human beings to suffer pain and misery until they die naturally and refuse them the decision for themselves whether or not to be euthanized.
Solitary confinement is psychological torture. We've long since discovered this with the first experiment of it at the Eastern State Penitentury in Philly. The idea had nothing but good intensions as the belief at the time was that isolation brought a person closer to God and thus would reform the prisoner, but the actuality was an epic disaster. Prisoners went crazy and committed suicide in unbelievable numers. Eventually, Eastern State understood that isolation only made people insane and changed their system to allow prisoners to interact and given more freedom of movement. Eventually, it closed yet still stands today rotting away. Since other countries modeled their prison systems after Eastern State with the same results, they also abandoned solitary confinement as a form of torture that did the opposite of rehabilitating. The US is the only country that has fallen back on the use of solitary confirement when history already has shown the results. Long term solitary confinement creates more dangerous prisoners and makes them insane. There is NO QUESTION that it is cruel and inhumane and that it is psychological torture. We've long since already learned this yet we're doing it again. We invented it, we learned that it made people more dangerous and crazy, yet we've gone back to doing it after everything we learned about it.