Let me take this a step further...

What if by some miracle of modern science or magic (just for the sake of argument) you could be 100% absolutely certain that this guy would never again commit any crime whatsoever. Not even jaywalking. He is no longer a threat to society, he will never again hurt anybody. Since he no longer needs to be segregated from society should he be let free? Do you see what I am getting at? Shouldn't there be a component of punishment? Is everything just about rehabilitation or protecting society, isn't there any room for being personally responsible for your actions?