What's so bad about Manic Pixie Girls?
I'd never heard the term before, so I had to look it up. And I've basically either never seen or barely remember any of the movies mentioned. (I mean, Fight Club had, well, fighting. I do remember the Eternal Sunshine of the Spotless Mind, but that was cited as not particularly Pixie.)
Anyway, I think I'd probably qualify as a real-life MPG (My husband: You? Wacky Hijinks? What? Me: We totally almost made it to Maine that one time.) Eh, I've got the hair, anyway. And my husband's kind of broody. And I totally like to think I'm his dream girl.
I take it that the dislike is due to the perceived shallowness of the character? (Honestly, I'm not all that fond of the characterization of something that I perceive as like me as shallow, though since I've not seen just about any of these movies, so I could be wrong, but it seems that very often if someone acts light-hearted, happy, or stereotypically feminine, they're seen as shallow, air-headed, bimbo, etc., while if someone acts more stereotypically masculine, they're mature and deep. I've had enough experience with people dismissing me because I'm female or act cute to get annoyed.)
At any rate, I don't think every character in a story needs to be a deeply-fleshed out, realized, meaningful character for it to be a good story. (Not even every dead character.) I don't kill my characters unless I have a very good reason to do so--I generally can't bring myself to kill anyone, actually, and have to go back and make myself kill folks off to make things more realistic, (because who ever heard of a revolution in which everyone calculated the odds before a battle and so the losing side simply surrendered without a fight?) so I have to remind myself that the characters *aren't* real--they exist only to be parts of the story.
It's only a problem if certain kinds of people appear disproportionately in such roles. Then we have a trend, and should give that some careful thought.
I really don't have enough data to go on, but I've truly never noticed a trend toward killing off characters of either sex. (Telepaths, on the other hand, never get to be real characters who don't die.) Perhaps that's just because I find the idea of finding one kind of death more meaningful or significant than another kind just weird. Wouldn't the death of any loved one be meaningful to the protagonist?