> My question, then, is this: if punishing people for crimes was shown to be ineffective for society, you would continue to support punishment?
> I think I must be misunderstanding. It sounds like you are saying that you’d prefer to cut off your nose to spite your face. (Punish criminals despite punishment being a net negative.)
No, you're not misunderstanding. To me your question makes no sense. By definition, a society that does not punish criminals is no society I want to live in. It is uncivilized.
If you mean, "if punishing people for crimes increases the number of crimes, would you still support it?" then my answer is yes, of course (though I don't accept the premise). Reciprocity is part of human nature. If you do something bad, you deserve to be punished in porportion.
To the extent that we adopt your perspective, the value of human beings will be lost. When you punish a criminal, you are treating him with respect. You respect that he made a choice, you are showing that he didn't have to make that choice and that he could refrain from making it in the future, and that by accepting his punishment he can pay his debt. I believe that this perspective will result in less crime but even if it doesn't, I'm still in favor of it because justice is an end in itself.