If he let Draco choose the red pill without obliviation, then Draco might tell Narcissa or other people, and the secret of Harry Potter would leak. He's asking for obliviation for security, and it's important enough that he needs to obliviate Draco even if he honestly chooses to stay Harry's friend and keep his secret.
"You're my friend, but I can't let you know that I killed your father, because you might tell that to someone else and that would be unpleasant for me."
Tell you what, I've made peace with this chapter. It shows Harry as a flawed protagonist, and in a more interesting way than Eliezer's usual "I was flawed because I was not smart enough".
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 120.
Plans for next chapter release:
There is 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.)