An example: I made a weak joke above about Justin Bieber. I have to confess that it is an uninformed bias — I’ve heard a song or two, but I couldn’t even name a single song by the guy, and I didn’t care for them. My personal dislike is not a sound basis for judging him, though, and it’s really a diss that can be safely made because of the opinions of all the other people in my bubble.
But if I cared more about the Bieber influence (I don’t, actually, you don’t need to write a dissertation), the opinions and evidence of musically informed people would be important. If there are good, strong, reliable reasons to claim that Bieber is derivative and untalented, a solid, detailed explanation for why a musician would think that would make me more informed about pop music, and I’d be better for it. On the other hand, maybe I’m wrong, and a musician would make a good defense for why he’s popular, what he does that is unique and interesting, and I’d be richer for that, too. Exploring dissent is a good thing that makes us stronger and better informed.
PZ Myers on expert opinions.