[I]f we lived in the sort of universe where horrible things were only allowed to happen for good reasons, they just wouldn't happen in the first place.

I love this line and am probably going to be quoting it frequently.

Edit: ...and Harry was pretty magnificent in that scene, in general. "Wrong! I want the secret of the Dark Lord's immortality in order to use it for everyone!" was one of my favourite moments, even if Harry was mistaken about the feasibility of that particular plan.