There’s some validity to the criticism. There are already too many movies about serial killers. The liberal reviewers, though, would have forgiven a lot if the movie had a liberal message.
There’s been enough reviews of the Joker so people know what they are stepping into when they go. Those crying out about it just want an excuse to flap their jaws.
I find serial murderers a fasinating study...like the Canadian Col. Russell Williams.... His interrogation was stunning and worth the listen..... of course some are just outright nutjobs and of little interest. BTK was another of interest. Bundy and a few others.