Moderators can't do anything here, this system just means that there will be a lot more arguing because the replies will be negative, reagardless of the overall toxicity level. Enabling users to display their disagreement with a comment directly has many benefits, how that effects how many people will see the comment is something else, but this is one of the things I really liked about reddit. You can still discuss if you want, but often you don't wanna waste time and/or get drawn too much into it. It is a more accurate measure of what people think about a comment.