The Vampire is a particularly apt metaphor.
What brings this to mind was an at Slate.com by one Grady Hendrix, where she berates the Twilight series for creating unrealististic expectations --- namely abstinence. She expects those girls to be putting out. Other sites discussing this essay include Double X, Jezebel, and others. I point out these sites because they are mainstream and not just someone blog. The comments are particularly interesting... they are largely in agreement. Not sleeping around is seen as devient and unnatural.
Of course, it is no secret that vampires and the erotic are so closely linked. Indeed, this is what makes the moral vampire such a powerful symbol. Normally a vampire is the very symbol of eternal lust, youth, seduction, power and vitality. But when part of this is forgone for moral reasons, it has much more of a message than just indulgence.
I am not a Twilight fan. Not a hater particularly, it just never really caught my interest for reading. But the idea of Edward as someone who is both moral, and yet vampire is a particularly apt metaphor for our times. It was pointed out (in the NYT?) that unlike other monsters that remind us of our relative frailty and mortality, vampires remind us of eternity and immortality - and what we could have.
The vampires in Twilight are viewed as strange for their morality in not wontonly drinking human blood. It is difficult for them as well - it is as though their very life depends on it.
Interestingly, Stephanie Meyers had a dream in which Edward told her she got it wrong, and that vampires did need human blood and that they could not truely live until they partook of it.
Is it so different with us? God asks some insanely difficult things of us - things that at times make us feel as though we are dying inside. Necessary? Oh, yes, but difficult all the same.
Another movie coming out (rated R, unfortunately) called Thirst, has a priest who falls prey to vampirism, and yet can not so easily brush off all of life's demands and responsibilities.
Marriage and sex are NOT things that made for our own self-satisfaction - and if we focus on that, as most vampires do, we will find our souls quite as dead as theirs.