Read "is OK to ..." to mean a cultural norm, not a judgement made by my or yours real values.
My argument is then: It's presently OK (in their culture); therefore (all else being equal) it's likely to have been OK in the recent past, and is not a recent innovation; therefore it matches the definition for being a part of their culture.
The last link to "therefore it's OK" that you propose is simply not necessary, I have already reached my conclusion.
Now if you read "it's OK" as meaning I, User:DanArmak, think it's OK for wizards to kill kittens, that would be a circular argument, and also a wrong one (because I don't think so). But that's not what I was saying.
The next discussion thread is here.
This is a new thread to discuss Eliezer Yudkowsky’s Harry Potter and the Methods of Rationality and anything related to it. This thread is intended for discussing chapter 84. The previous thread has passed 500 comments. Comment in the 14th thread until you read chapter 84.
There is now a site dedicated to the story at hpmor.com, which is now the place to go to find the authors notes and all sorts of other goodies. AdeleneDawner has kept an archive of Author’s Notes. (This goes up to the notes for chapter 76, and is now not updating. The authors notes from chapter 77 onwards are on hpmor.com.)
The first 5 discussion threads are on the main page under the harry_potter tag. Threads 6 and on (including this one) are in the discussion section using its separate tag system. Also: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14.
As a reminder, it’s often useful to start your comment by indicating which chapter you are commenting on.
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: