A method to their madness: Dara Naraghi points to an interesting essay at Kuro5hin.org about the madness at the center of the Batman universe:

"... Indeed, a remarkable number of Arkham inmates have been driven to madness as a result of their work as investigators of the human mind. Several are psychiatrists; Harley Quinn, originally Dr. Harleen Quinzel, is portrayed as an ex-Arkham psychiatric intern who fell in love with The Joker. The influence of her patient caused a folie à deux reaction causing her to abandon her previous life and personality. The fictional creator of Gotham's forensic psychiatry centre, Amadeus Arkham, fared little better. He was originally a psychiatrist who converted his gothic childhood home into Arkham Asylum out of a desire to help the criminally insane and lost his mind as a result. An enduring character from Batman's early years is Professor Hugo Strange, a psychiatrist who became obsessed with Batman to the point of insanity and now seeks to destroy him. A more recent example was given in the 2003 series Arkham Asylum: Living Hell (a title that speaks for itself) where the initially sympathetic psychiatrist turns out to be shape changing psychopathic criminal in disguise! Psychiatry it seems, is not a profession that produces pleasant thoughts for the writers of Batman."