If you treat prisoners well, they will be less angry, less inclined to violence inside prison, less likely to provoke violent actions by guards, less likely to have reason to file brutality lawsuits that cost taxpayers a bundle and waste administrators' time. And most important, well-treated prisoners will be less likely to leave prison angrier, more vicious and more inclined to criminal behavior than when they went in.
History is full of people who went to prison or were burned at the stake for proclaiming their ideas. Society has always defended itself.
Written laws are like spiders' webs, and will, like them, only entangle and hold the poor and weak, while the rich and powerful will easily break through them.