's "The Killing Joke" is remembered by most fans
as the ultimate Joker
story, due to the graphic violence
and mature content
, which elevates it above the typical super-hero comic's mindless slugfest
and uni-dimensional plotline.
Read on the surface layer alone, this is quite true. With the exception of Frank Miller's The Dark Knight Returns and Batman: Year One, very little mature work suitible for adult consumption has been done on Batman, and as such, any work that raises the bar to something approaching actual literary quality must be approved of by the audience. We cannot be expected to consistantly enjoy a character who, although a "crimefighter", never experiences anything like real world crime...Consider that, since the publication of the these three graphic novels, Batman has become ever more grim and gritty, and now has an edge to him that would have made readers of the sixties and seventies wonder "Where did the happy go lucky Caped Crusader go?"
But like most of Moore's work, this is a work that also has more depth than most (hell, almost ALL) comics would ever even dream of achieving. Moore, who learned how to write not from comics, but by reading actual literature (a lesson almost everybody in the buisness would do well to take to heart), often weaves several layers of commentary to his stories, and it's worth your time to investigate them.
In order to avoid repeating what some of the other noders have pointed out, I'll get right to some of the "deeper" meanings. To begin: Consider that Batman, as a fictional character, exists in a static universe, where nothing ever truly changes. The fact that Batman is an ongoing series of comic books, that must, month after month, sell X number of copies in order for the buisness side of it to make any sense, means that you can never be absolutely free with the kinds of stories you tell. Batman can never rape Catwoman, for example, and not just because that would be "Going Against His Character". No, Bats can never brutalize Catwoman because it would change the comic too much, and fans would drop the book like a bad habit.
Similarly, the much heard axiom that nobody stays dead in super-hero comics is axiomatic for this same reason. If the fans want a character back, and are threatening to drop the title, the suits in charge (and they ARE in charge, remember that DC Comics is owned by Time-Warner) can reverse even the most poignant tale of demise and reinstate the deceased to the healthy bloom of life at the proverbial drop of a hat.
What does this have to do with "The Killing Joke"? Everything. See, that is what is really going on here, amongst the brutality and the torture, and the carnival of freaks. In this story, Joker pushes the limits of everything that is sacred. He pushes Batman and James Gordon to the very limits of sanity, and it's pretty damn clear that any rational person would kill him for his vile deeds. (It might be different if this was a first time offense, but think about it: Everytime the Joker goes out and murders a gaggle of people, the only punishment he receives is a trip back to Arkham, where he will, of course, escape from again to kill even more people)
Batman's opening dialogue with the fake Joker at Arkham says it all...and sets up what should have been the climax of the story. Quoting from the story: "Are you listening to me? It's life
and death that I'm discussing here.
Maybe my death . . . Maybe yours
. . .
." (Thanks for the link, TenMinJoe)
Moore's meta-commentary here is as follows: Batman should kill the Joker, but he can't, because the status quo must be maintained at all costs. It follows that there will never be any real character growth for this character. He will forever be trapped in a cycle of violence, never to escape. Batman's seemingly inapproprate laughter at the Joker's escaped inmates joke at the end of the comic is possibly the dark laughter of existential horror, as he briefly realizes the utter futility of his existence: He exists only to amuse an invisible god who delights in his misery. Because the sales must keep up, he will never, can never, escape. In this regard, this story applies to all super-hero comics...Superman's Neverending Battle is axiomatic hell for all of them.