I disagree, because I see these factors as necessarily closely connected, in any person's mind. I rate not quality of prose, but quality of communicated idea, as it comes through. If I think that the idea is silly, I rate it down. If the argument moves me, communicating a piece of knowledge that I at least give a chance of changing my understanding of something, then the message was valuable. It doesn't matter whether the context was to imply a conclusion I agree or disagree with, it only matters whether the idea contributes something to my understanding.