Levels of Difficulty

The discussion about whether WoW has become too easy or not is hardly new, but Mimetir, a guest poster over at World of Matticus brought it up again. This prompted Larísa to write a strong post on how she's sick of hearing people claim that WoW is too easy these days if they haven't beaten all the content yet.
She is correct in many points and I'll address that below, but here's one thing I am sick of: People claiming that just because there is something left that I haven't managed to do yet, the difficulty is fine.