Thomas Shey
Legend
That dismissal--which tends toward (or at least gestures at) "that sucks because it's popular"--is what I'm talking about when I say it's the same fallacy.
I think--sometimes--popularity is a worthwhile thing to look at, but I think it's as likely to point up matters of popular taste (including trends and other Zeitgeist-type effects) as much as the actual quality of a given work. I'm not going to dismiss someone--author, musician, filmmaker--just because they're popular, and if they stay popular for at least a chunk of their career, that does seem as though it says ... something ... even if that is just "They're really good at being popular."
The only thing I have with arguments about quality demonstrated by popularity is, depending what it is, there can be a whole lot of factors in play that make something popular, and quality is only one of them. But people will take it as a given that its the most important one. This doesn't mean in some cases quality isn't the biggest reason, but you just can't take that as a given.