I understand that sometimes something strikes you as so bad, you can't help but nitpick and tear it apart on every level. And then I also remember one of Film Critic Hulk's essays about how a lay audience can realize a work is bad, but the majority don't really have the knowledge or training to really explain or understand the fundamental reasons why it was bad, and so end up harping on a superficial things they'd probably forgive in a better work.
I think the argument is that if you scratch deeply enough, you can plainly see all art and fiction is artifice and illusion, and all of it has some plot holes, or inconsistent characterization, or factual errors, etc. In works that "work", you bother your enjoyment [http://tvtropes.org/pmwiki/pmwiki.php/Main/FridgeLogic]. But in works that fail fundamentally, almost every little thing will become a glaring flaw.
With regards to Twilight, I have no problems with people bringing up the stupid characters, the plots where nothing happens, the sexual politics, etc. I get annoyed when people start arguing "vampires and werewolves don't work that way", as if zoologists have observed these fictional creatures in their natural state and made broad conclusions about them. I get this from the vampire LARPers I used to hang out with, many of whom perfectly accept that vampires from different fictional universes almost never work exactly the same, but for some reason Twilight is the one singled out for this.
CAPTCHA: It is different.
You're damn right, Captcha!