All sold out
The question of whether pop musicians have sold out never seems to get old, even though it seems as though no argument is possible: these are professional musicians, who intend to make money by selling their product. Perhaps our joy in music is feels so direct that we can't imagine calculation in its making; we presume the musicians feel as straightforward and unguarded as we do toward the music. We don't want to imagine them calculating just how to manipulate our emotions and coax dollars out of our wallets.
So it's perfectly understandable that we would want to mythologize pop music "artists" and regard them as being true to some autonomous purpose (as Yglesias highlights) other then selling more Coke (though the history of pop-music Coke themes is long). And the listener's vicarious appreciation of a song is radically diminished when a product is shouldering in to claim some of the song's signifying potential, to colonize some of the space for fantasy a good pop song evokes. It feels like theft when you've bought a song hoping to make it about yourself, only to discover that the band's sold it elsewhere to make it about jeans or cars. Of course, there are probably many who feel validated in having something they like be adopted by advertisers -- it suggests maybe they too could make it as musical supervisors. But typiclly we feel some blend of the two: for example, until a month ago the name Dave Dee, Dozy, Beaky, Mick & Tich meant nothing to me other than that they sang the idiotic "Zabadak" in the 1960s. Then I saw Grindhouse in which their song "Hold Tight" is used. I think the song's pretty great, and I'm grateful to Tarantino for using it, but I'm also annoyed that every time I hear the song I have to think about Tarantino and that idiotic film. I can't form my own mental picture for a song I'd probably never have heard in the first place if not for Tarantino's strong intention to use it to convey his mental picture.
Anyway, I agree wholly with Scott Lemieux, who points out that authenticity is an absurd criterion, since there is not a way of convincingly conveying it without becoming wholly inauthentic in the attempt. Authenticity doesn't sounds like anything in particular; instead we apply it to sounds we like as a way of bolstering them ideologically and enhancing our enjoyment. So I would argue that only listeners can be authentic or not -- working musicians can not be in bad faith. Listeners can knowingly begin listening to music to accomplish something other than aural enjoyment. (It gets more complicated when you admit the possibility that these extra-musical motives could be subconscious.)
And Amanda Marcotte is right that filesharing has permanently altered the terms of conditions of being a professional musician. Without being able to rely on the music companies for a steady income stream, musicians have take money where they find it, and probably need to be open to alternative ways of garnering publicity. I think this is why its harder for musicians to claim to be above commercialization -- they no longer have an effective and powerful music industry to run interference for them and promote the fact that the bands are not selling out.