As a self-avowed elitist and terrible snob, I tend to utter phrases like "broad mainstream appeal" with the sort of tonal qualities that clearly imply I consider catering to that demographic to be every bit as appealing as wading hip-deep through an ocean of shit.
But for all my snobbery and only semi-sardonic use of tautologies to support my argument that the only opinion that matters is mine and I am always right because I said so (ha ha!), I don't actually hate "mainstream" things because they are mainstream. It's more that I came to realize the simple truth long ago that people are bloody stupid, and the larger the group, the lower the aggregate intelligence in the audience will be. Ergo, things that the huge clamoring masses of humanity like tend to be stupid crap, because the lowest common denominator out of a vast teeming swathe of humans is a moron. It's simple math really.
But with that said, not everything that is popular or well-known is worthless, and obscurity is hardly a guarantee of quality - some things simply possess universal appeal, and they deserve their popularity because they are good; the legions of stupid people that also like those things is merely incidental in other words. Sometimes simplicity is elegant rather than the clear result of "dumbing down", sometimes approachability is awesome instead of insulting, sometimes things are just good, and pretty much everyone can recognize and appreciate those qualities.
Hating something for no other reason than because it is well known and well liked, regardless of whether or not it deserves that recognition, makes you a hipster, and a hipster is just a different, far far more pretentious variety of moron who can't see how ridiculous he is. Hate things because they're stupid or otherwise crap, not because people have heard about it.
