I think (or at least hope) the main cause for concern in the US not that it will make the law worse, but that it takes the law out of our hands, so any problems with current law become almost impossible to fix. When there's an over-broad law, it's possible (and sometimes it even actually happens) for Congress to recognize the mistakes in the original law and dial things back a bit. But once it's in a treaty, Hollywood kind of has DC over a barrel.