Which sent me to the latest edition of Kevin Smith's FATMAN ON BATMAN podcast. The relevant section being at about 1:07:35 mark.
"That's why it's called The Killing Joke. The Joker tells the 'Killing Joke' at the end, Batman reaches out and breaks his neck, and that's why the laughter stops and the light goes out, 'cause that was the last chance at crossing that bridge."
In brief, The Killing Joke functions as a origin of The Joker, presenting him as a two-bit, failed comedian, recruited by some hoods to aid them on a heist of the Ace Chemical plant, where our unnamed comedian used to work. The comedian, unable to secure paying comedy work, with a wife to support, and a child on the way, desperately needs the money. The criminals give him a "Red Hood" to disguise him during the crime (The Red Hood was revealed in Detective Comics #168 [Feb 1951] to be The Joker's original criminal guise). During the course of the story, his wife (and child) are killed in a bizarre bottle-warmer accident, he's forced to complete the heist despite this, and he's dumped into the famous vat of chemicals. Emerging as The Joker.
That's flashback. The contemporary story involves The Joker kidnapping Commissioner Gordon, in the process shooting his daughter Barbara (traditionally also Batgirl - but that's never mentioned in this story), taking him to a dilapidated carnival and sideshow. He tortures Gordon, shows him pictures of his maimed daughter. Stating over and over again that his goal is to drive the Commissioner insane.
The MOST relevant line for this discussion? The Joker says:
"All it takes is one bad day to reduce the sanest man alive to lunacy. That's how far the world is from where I am. Just one bad day. You had a bad day once. Am I right? I know I am. I can tell. You had a bad day and everything changed."One. Bad. Day.
How else can you describe what Batman endures? His best friend kidnapped, beaten, tortured. His friends daughter (and possibly one of his crimefighting partners), defiled and paralyzed. All by a man who he has, repeatedly, captured and incarcerated. A man he has, repeatedly, refused to kill, either out of pity or his own moral code.
Flat out, Batman is indirectly responsible for the monster called The Joker existing in the first place. He's also repeatedly refused to permanently end his monstrous work. Now, "one bad day" later, those facts have driven him over the edge.
He kills The Joker. Flat out breaks his neck. The laughter on that page stops abruptly, because the joker is now dead, in front of the arriving police sirens. Even after Gordon had warned Batman that it had to be "by the book," to prove to The Joker that the system still worked. The Joker has finally driven his eternal opponent insane.
The Joker wins, even in death.
I've always liked The Killing Joke a whole lot. A whole, whole lot. However, I've resisted it as "the best Joker story, ever" for a lot of reasons. Frankly, I've always felt that Denny O'Neil and Neal Adam's "The Joker's Five-Way Revenge" (Batman #251 - Sept 1973), or Steve Englehart and Marshall Rogers' "The Laughing Fish" (Detective Comics #475 - Feb 1978) truly deserved that crown.
However, this re-evaluation of The Killing Joke's ending changes all that. Mainly because it becomes, literally, the ULTIMATE Batman/Joker story. There can be no more. It's also a deeply unsettling and twisted tale, as all Joker stories should be.
It also makes The Killing Joke EXPLICITLY outside of continuity. Which is the grandest thing of all. Even at 17, when the book was originally published, I felt like what Moore and Bolland had crafted should not, in any way, be tied to the regular books. When Barbara Gordon was suddenly confined to a wheelchair in the regular Batman and Detective Comics monthlies, I felt that The Killing Joke had been cheapened.
I've read a few attempts to debunk Morrison's reading, and I find them just as flawed as those who take umbridge with Christopher Nolan's film trilogy. The fan brain seems to be unable to process the concept of "outside continuity." This obsession with determining if stories "count," or not, is just terribly problematic. There needs to be a realization that truly great stories rarely appear when they have to connect A to B, or worse (and part and parcel of the serialized fiction world) connect A right back to A over, and over, and over again.