This was exactly the problem. Maybe 1 in 10 threads was something other than insulting one of the actors or some form of trolling. Many of the threads are just spam or totally unrelated to the movie. I don't see why these couldn't just be removed.
These low quality are almost entirely by new accounts. It would have been much smarter for them to have some kind of moderation system than scrapping it all together. For example give mod rights to older accounts that have written reviews with good feedback. They should have tried some kind of crowdsourcing before totally scrapping it.