Does it not all just boil down to taste? Eventually you discover music that moves you (or makes you move) and it becomes important to you. I say eventually, because when you're young that's only part of it - there's also fashion, wanting to be in a 'gang' etc. Its no less important (to the individual) for being about more than just the music, but most robust battles fought out in the playgrounds, letters pages of the NMA, forums etc are, lets face it, pretty unsophisticated ("Blur are s**t, Prince is God" and so on ad nauseum). I've reached a point where I can listen to any sort of music, work out whether I like it or not all by myself, and genuinely don't care or even think about whether it is "credible" or "authentic", "genuine" or "manufactured".