I consider the following to be true:
a) In some sense, people experience things. People suffer. Punishment is unpleasant.
b) There is no such thing as free will
c) There is however something rather akin to free will whereby the brain in its whole can make decisions and decide to do something, or not do something, and some of said decision has to be based on potential punishments.
So what do I think this means? To me it means quite simply that punishment to make the criminal suffer is wrong. I do not have a problem in principle with punishment to act as a deterrant, either specific or general, but it’s only part of things.
In an idea world, sentences would either be about removing someone from society, or “re programming” them.
There would never be any suffering and convicts should have a pleasant time.