The thought of mentioning other reasons why to punish (such as to make people behave more to your liking) did cross my mind, but I thought it was obvious enough. In fact, there are still other reasons to punish. Someone might reply to your post, "You are thinking like an engineer. I am thinking like a social animal. I want to know when I should punish: I want to use my understanding of social dynamics to make people respect me more. I want to know what it signals about me when I punish someone."

As I said here, there are a lot of different reasons to use moral language (most of them sort of dark-arts-ish, which is why I guess that post was downvoted), and likewise there are a lot of different reasons to punish.