Basically blame the New52 for the way Harley is treated by fans now. Prior to that she was a popular but minor character in the Batman books. I think she was in a team book with Catwoman and Poison Ivy called Gotham City Sirens that ran until the reboot, which did do a good job of breaking her away from the Joker for a bit.
Come New52 and they put her on the Suicide Squad, dumped her old costume for the Hot Topic look, and basically she became really popular all of a sudden. Then they put her in the Suicide Squad movie, which I think is when people started calling her a feminist icon and conveniently forgot her backstory where she slept with her teachers to get her degree and was the poster child for battered girlfriend syndrome.
Of course, even back in the day when they paired her up with Poison Ivy instead of Joker she was still in an abusive relationship. Ivy would always act like the really possessive girlfriend who didn't want you talking to all your old friends and trying to control your every action.