Ah yes, the classic "middlebrow dismissal".
Sometimes refutation comments are good and valuable though.
In general the decisive factor in the value of a comment is what I will call the "lebowski rule". If a comment contains a statement of someone's opinion and nothing more it is rarely worthwhile.
By way of illustration, this comment would fit that criterion up to this point.
However, I will explain my reasoning which will hopefully rescue it. In the internet age most people are aware of the variety of opinions on a topic, especially the most obvious pro/anti points on a given topic. What can often happen on sites like reddit or HN is that the first comment that espouses a well-known opinion then becomes effectively an impromptu poll. This breaks the link + comments model though because the opinion of the link is inherent in the link itself so a post voicing unadorned agreement would be easily recognized as valueless and thus generally not created or voted up. Whereas the contrarian opinion has no representation and thus becomes the proxy poll for disagreement. The problem is that people voting for/against place their votes differently, either for the link or for the most popular "middlebrow dismissal" comment. But because these are two separate beasts they can't compete against each other directly. Which is why you get the behavior of highly upvoted rejection comments, since that is effectively a reflection of the controversy around the subject. Even though that rarely improves the level of discussion.
In contrast, a more thoroughly thought out refutation which follows through lines of reasoning and evidence will be more likely to contribute to both the disemination of new knowledge to readers as well as higher quality discussions.
Additionally, the mere attempt to try to improve the quality of a comment through fleshing it out will lead to a higher rate of abandonment of less worthwhile posts.
P.S. Here is one area where I think the HN software doesn't help, because it encourages shorter, more quickly written posts which tends to favor the exploration of shallower depths of thought.