I agree to an extent. These characters are fluid. Retcons and reality altering events change them and wipe out entire stories. Sure, Joker was abusive to her. Who is he not abusive with?
My point is I learned a long time ago to be cautious with what writers do with these characters. When I take issue (as a survivor of trauma myself) I make sure it’s with the creative teams. Like Tom King and the well intended but poorly handled Heroes in Crisis.
I don’t dislike Wally West as a result of the story. I dislike King’s depiction and use of the character. I dislike Joker’s treatment of Harley, but choosing sides in a fictional romantic relationship seems a bit extreme. That’s my take anyway.
These are supposed to be fun characters to be involved in. The moment the way they treat one another starts to make for toxic fan base division; then it’s a problem.