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It's worth breaking (1) up into two parts:
None of this affects your main point much: that in any case #3 is very important to Harry. (So I vote you up regardless.)
[Obsolete material follows.]
You ask what's the purpose of punishment, and one of your answers is punishment. I have two hypotheses towards what you actually meant:
What's the purpose of imprisonment?
- Punishment.
and
What's the purpose of punishment?
- Revenge.
Did you mean one of these, and if so then which?
I'm pretty sure that one of the common purposes of punishment is to make the people who are imposing it feel better. This may or may not be a glitch by some utilitarian standards.
Update: Discussion has moved on to a new thread.
After 61 chapters of Harry Potter and the Methods of Rationality and 5 discussion threads with over 500 comments each, HPMOR discussion has graduated from the main page and moved into the Less Wrong discussion section (which seems like a more appropriate location). You can post all of your insights, speculation, and, well, discussion about Eliezer Yudkowsky's Harry Potter fanfic here.
Previous threads are available under the harry_potter tag on the main page (or: one, two, three, four, five); this and future threads will be found under the discussion section tag (since there is a separate tag system for the discussion section). See also the author page for (almost) all things HPMOR, and AdeleneDawner's Author's Notes archive for one thing that the author page is missing.
As a reminder, it's useful to indicate at the start of your comment which chapter you are commenting on. Time passes but your comment stays the same.
Spoiler Warning: this thread is full of spoilers. With few exceptions, spoilers for MOR and canon are fair game to post, without warning or rot13. More specifically: