What else could you possibly mean other than absolute basis?
I can call Gandalf morally superior to Sauron (1) on the basis of my moral standards.
If I'm understanding your question correctly, you think I can't possibly do this; that my own moral standards aren't sufficient basis for calling Gandalf morally superior to Sauron; that I have to invoke an absolute morality in order to do that.
Is that right? I have to admit, that strikes me as a silly idea, but I assure you I'm not mocking you here... I can't come up with any other interpretation of your question. If you mean something different, I'd appreciate correction.
(1) Actually, it has been long enough ago since I read LoTR that I'm not actually certain of that judgment... I can't recall what Sauron actually did beyond being everyone's chosen enemy. As I recall, we don't actually get to see much of Sauron's activity. But I'm assuming for the sake of the argument that if I reread the books I would in fact conclude he was morally inferior to Gandalf.
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: