I mean, won't say if I agree or not because I haven't seen the movie yet, but what some are criticising isn't just "movie's violent and therefore people seeing it will replicate the violence". I agree that would be dumb. The thing is, Joker is being criticized by how it frames the violence, possibly justifying a character that has no business being justified because "society". Taxi Driver made it pretty clear Travis was a lunatic who shouldn't be idolized and serves as a cautionary tale. We can't know how Joker frames its protagonist without seeing it.
Again, I'll reserve my judgement until I actually see the movie, but let's not blindly defend it, too. Maybe you'll love the movie, maybe I'll love it too, there's certainly many critics who do, but let's not get ahead of ourselves.