People never consider the cultural context of when characters are created. The last two decades prior to Harley's creation had seen a rash of high profile serial killers like Ted Bundy and Jeffry Dahmer. Many of these guys had active fan bases of women who saw them as tortured souls, Bundy especially was considered a handsome charmer despite preying on women, he even got married while incarcerated. This phenomenon of people who romanticize danger when its at a controlled and safe distance weaves its way through every modern fandom, because it's a fantasy, but sometimes they become so wrapped up in the fantasy that they ignore the red flags which is exactly how people get trapped in actual abusive relationships. They thrive on the highs of the early courtship, clinging to the memory of the good times not recognizing that was all just a veneer for the true nature of the abuser, and every crumb of sweetness they dish out is little more than a booster shot to keep the victim holding out hope. What's more around the 80's there was a resurgence of satanic panic where a lot of shady psychologists and shrinks were looking to get rich off a book with their flimsy diagnosis of people's evils. Harley was a pastiche of these elements, an opportunist with no real interest in the psychiatric field beyond the high profile notoriety, who fell in love with a man she didn't truly understand, and stuck around because she was in too deep to quit.