You can't craft good policy that way. Rehabilitation, low recidivism, etc are far more important than revenge in optimizing the global situation.

It's better this one killer serve out a sentence on their PS2, away from society, than creating 10 killers in the first place and executing them to satisfy bloodlust.

If anything I'd argue that he should have been put away for more than 21 years since he'd certainly still be a risk to the public, but as it turns out after the 21 years they just extend his time anyway as long as he is still deemed a danger to society and that seems perfectly reasonable. I suspect he'll always be deemed a danger to society, but if turns out that there's some reason why that changes then why shouldn't he be released?

I also don't care if he spends his time locked up playing video games. I hope that as long as he's locked up he is well treated and somehow lives an otherwise happy life. If I'd done what he did I'd never find peace. Some people just can't be allowed to be around the rest of us, because if we let them, they'd harm us. Keeping them imprisoned and unable to do as they please, go where they want, and be with the people they love is punishment enough but that's what is needed to keep the rest of us safe. If we had some means to "fix" people broken in the way he is so that they wouldn't go around murdering a bunch of people we wouldn't even need to do that.

I'm not at all interested in torturing or murdering people out of a desire for revenge. It's a tragedy that he murdered all those people, and it's another tragedy he'll have to spend his life locked away from the world because of it.