Criticism, yes, I just think a more enlightening reply would do more for the conversation. The way I like to think of it is that you're refuting an argument for the benefit of other readers of the comment who may not be well informed / are persuadable, rather than to oppose the person you're replying to. Think of it as communicating a thoughtful missive to someone (who honestly doesn't know) that has asked you "what's wrong with that comment?"