‘Canonicity’: the Book or the Reader?

[Bêthberry]

To expand the question, would a fanfic which presented Sauron or Saruman as heroes, & was approving of their actions be 'canonical' as long as it stuck to the historical 'facts' of LotR, or would it be 'uncanonical' because it went against the moral values which Tolkien espoused?

To my mind, a fanfic or an RPG could very profitably and canonically explore Sauron's or Saruman's or the Nazgul's "fall" as long as it demonstrated Tolkien's abhorrence of power when used for domination. The question turns on what we would agree is the moral value Tolkien espouses in the books. It is an interpretive act.