How many percent of music revenue comes from "true" music listeners, do you think? That's a pretty weak argument. I don't know about Pandora, but Spotify has a stunning array of music (maybe it's different in the US). Yeah, I don't find absolutely everything I'm looking for, but they have probably more than 80% of the music I listen to, and I listen to a lot of lesser known stuff.
I wasn't arguing anything for the artists, I'm talking from a listeners' standpoint. If I never find out about bands outside of Pandora's library, nobody is at a loss, because I'm not the kind of person who would have found those bands anyway. i.e. If I'm going to spend all my money on a Lil Wayne cd, you can't make the argument that hip hop is killing 'real music' because I'm obviously not in the market for the Velvet Underground in the first place.
Pandora really isn't the main "problem", Spotify is the real threat. You can find all sorts of obscure stuff there. I don't know where I fall in this debate, though. I frankly use Spotify a lot, and I pirate a lot of stuff too.