Quote Originally Posted by Soulforged
All those purposes can be grouped in the first two. The third is exactly what you don't like (and I either for that matter) but some judges do: "retribution".
No it isn't. Retribution is an emotional response. Exclusion is purely functional. While a person is in prison he or she can technically not reoffend (with exceptions). Thus excluding people who are prone to harm society is a means to protect society. This has nothing to do with retribution, it could rather be compared to quarantine.

It is all a thin veneer over thousands of years of evolution. People that repeatedly act as though the veneer has been removed should be treated as such.
There is no veneer of evolution, at least if you look at evolution of genes and memes. But I understand your reasoning. I understand it but reject it, because I do not think that it is beneficial for society. What would we gain from treating criminals like they treat others? You cannot discourage violent behavior by being violent. Our society would only become more martial, rather decreasing our safety.