I once worked with a guy who was a pretty harsh critic about everything-smart as a whip, this guy, but nearly every book, band, and movie failed to measure up to his exacting standards, and he used superlatives rarely, if ever. I'm sure you've met a few people like this yourself, right? These critics run on a dark energy that would corrode most of us mortals and rarely do they actually create anything noteworthy themselves, preferring to scoff at the imperfect creations of others and praise only the obscurest works by the obscurest artists, somehow thriving on the meager feed of knowing shit about shit that nobody else gives a shit about.
You can speculate what actually goes on in the mental depths of these characters, and call them names like nerd or hipster or elitist, but surely they must exist to balance out the mouth breathing bubble heads who consume anything, praise anything, as long as it demands little of them and makes the time pass in a shiny way. What you cannot do, as any kind of artist, is let this same mentality gain too great a foothold in your own soul. It's fine to be discerning, and to read all the literary criticism under the moon above, but as soon as you turn into a true cultural snob you're headed down a dark and masturbatory path.
Why is, Blogagaard? Well, for one reason, every time you criticize anything, you are to some extent asserting your own superiority to it-maybe you couldn't do it better yourself, but that's just because it doesn't happen to fall in your particular field of talent or interest. And sure, this is fine in small doses (and everyone is entitled to their own goddamn opinion), but sooner or later you begin to cut down one too many paths, and it's a writer's job to keep as many paths open as possible (or avenues of thought, if you will). It's fine for a bitter old hipster with a day job to rail against everything as "mainstream" and "trite", but if you peel away enough layers you'll run out of onion, and if you deny enough of the world you'll soon run out of world to talk about (at least in any meaningful way).
So go ahead and rail at shit fests like Twilight and whatever else is currently on the bestseller's list, but don't lose sight of the fact that their must be something to them, something you can use in your own authorial arsenal that resonates with your once and future readers.