There have always been the 'think of the children' types, usually barren women well past middle-age with nothing better to do. But here we have relatively young and left leaning people doing the pearl clutching and I'm left scratching my head wondering why. Are they really all just butthurt that this movie about a demented clown's spiral into insanity is way better that the shitty sassy whaman
The logic doesn't make any sense except you have to think of SJWs in a creative sphere. They hate the Joker for several reasons:
1) White men can never be victims. White men must always be cartoonishly evil. Arthur being poor, abused and mentally ill goes right up against all of their narratives. Its as much as dealing with false rape accusations in Shield Hero (which are far more common than they like to think) and to outright rape in Goblin Slayer (as in, what do you think petty evil creatures would do to the women they captured?). SJW media is basically just propaganda. Anything that disputes their propaganda must be vilified.
2) SJWs believe that if you see something, you will emulate it. They believe that imagery and ideas are like a zombie virus, where if you see it in something resembling a positive light, you will imitate it. They have no belief in independent thought and believe you can be brainwashed by pop culture, which is generally impossible. Brainwashing is, in and of itself, almost utterly impossible except at the end of a gun. People who are 'brainwashed' are generally just sheltered and refused to be exposed to other ideas on their own. To be frank, people become brainwashed because they want to. Being part of a mob that is never wrong, lets face it, feels really fucking good. Being part of that group is self-reinforcing. Its basically institutionalization, like with criminals. They're held hostage by their own mentality so they need to be in that little box. The world is too big and frightening for them, and that small, narrow box of their minds is much safer. They believe everyone is like them, so they clamp down hard.
3) SJWs posses no ability to empathize. They cannot put themselves in the shoes of anyone else, which is why they get so much wrong about the world, and their own institutionalization and desire for simplicity in complex ideology shuts out women, minorities, LGBT folk who challenge their narrative.
So you put these three factors together, its not hard to see why they dislike the movie so much. They're mentally stunted fucktards who can't empathize or understand anything outside of their small bubble and believe you can catch ideas like a virus.