I would include the new book
Batman and Philosophy: The Dark Knight of The Soul. It's the latest in the series that includes
Metallica and Philosopy and
Battlestar Galactica and Philosophy.
Batman and Philosophy is a collection of 20 article or essays from various contributors on all the big
Batman topics, starting off with "Why Doesn't Batman Kill the Joker?" There's also:
"No Man's Land: Social Order in Gotham City and New Orleans"
"Alfred, The Dark Knight Of Faith: Batman and Kierkegaard"
"Why Batman Is Better Than Superman"
... and lots more.
You do not need a Philosophy degree to enjoy this book. Of course, possessing such a degree wouldn't hurt.