A short article I wrote on this topic has now been posted at the Shelf Abuse site. Thanks to Carl Doherty for arranging this. An extract is below:
Long decried as reductive and simplistic, comic books are actually, as Douglas Wolk has recently suggested, a vehicle peculiarly suited to allegory: that is, to the representation of abstract ideas through narrative. Wolk argues that superhero comics in particular ‘provide bold metaphors for discussing ideas or reifying abstractions into narrative fiction. They’re the closest thing that exists right now to the “novel of ideas.”’ (Wolk, Reading Comics, p. 92) All superhero characters and plots are, in some sense, allegorical, but this in no way detracts from their integrity as stories.