In reference to your first question, one is acceptable to almost all of society, the other is abhorred by almost all of society. So you can make your own mind up on that one.
So your argument is that society is correct by definition? Isn't that a tautology?
There have been other societies (including colonial American society) where prison was seen as cruel and unusual punishment, and that punishments should be swift, rather than dragging on for years or decades.
The whole point of jail is that it is meant to be good conditions to rehabilitate the prisoners. At one end of the scale you have some European prison systems that do this amazingly well, with very low recidivist offender rates. At the other end of the scale are some third world country prisons where the prisoners are kept in horrendous conditions.
So a tiny minority of prisons worldwide are doing it right? While the vast majority are horrendous? Doesn't that indicate that society is wrong? America has 25% of the world's incarcerated population, with just 5% of the global population. Our society seems happy to have shitty prisons and people locked up for decades for possessing a plant. Seems to me that going by what society thinks is a bad idea. Nazi German society thought it was a great idea to murder people by the millions just for being different. Aztec society thought it was cool to have human sacrifice.
Your logic is completely broken: in one post, you argue that just because a group of people ("society") decides to murder someone doesn't make it right, but then you argue that just because society decides to lock someone away for decades and torture them, that that's perfectly fine. You can't have it both ways.