the truth? you can’t handle the truth!
batman is the joker. he always was. batman’s origin story is tied up with the joker. he was formed as the joker was. they are mutually dependant on each other because they are the same. they are one. I am not talking about some plot twist, some Tyler Dirden thing.
no. batman the superhero as a personification of Bruce Wayne lives to hunt down badguys. they are all evil and twisted and responsible for so much pain. but in batman's mind, they are lesser exsmples of the architype Joker. he can kill the fakers, but he can't bring himself to kill the real guy. he depends on him existentially. without joker, batman will be nothing. he had many opportunities to end the game, but always chose not to go through with it. not because of some high morality or a wish to see justice done, but out of fear. he knows the truth and bitterly gives in to his justifications.
he is just as crazy in many ways.
joker has the same problem. he can kill innocents, police officers, authority figures, even sidekicks. but he knows that the fuel to his rage is his life and what brings him rage is the thought that batman is still around. he self sabotages his own schemes just to leave an out to batman.
imagine if one of them died. how will the other go on?