I agree that it's important to point out things that are actually harmful. That quick rebuttal needs to include more than a snarky snipe, an insult, or a statement that "No, you're wrong." If that's all that's being added, you may as well just downvote, which is, among other things, an indication that the comment isn't a worthwhile contribution.

To be useful and more than noise, it needs to actually rebut the point in line or pointing to additional resources. HN is pretty good on that point: the community is large enough that it's going to get addressed well. Quality of conversation and quality of information needn't be at odds, and both are addressed in the guidelines.