A MG/YA editor once explained to a workshop group I was in that the popularity of teen vampire novels is related to a young female reader's fascination with "bad boys." So reading about a young female protagonist romancing a vampire (or werewolf or zombie or a ghost) lets the reader experience the excitement of being in a relationship with someone others might not approve of.
Sometimes bad boys fascinate girls, especially "good girls." It happens in real life, it happens on TV, in movies, and it happens in young adult and even middle grade literature.
In WEST SIDE STORY, Maria wanted to be with Tony even though he was a member of her brother's rival gang. Similar story in ROMEO AND JULIET. The couples' forbidden attraction only made them want each other more.
There's a lot of fan fiction out there on a Hermione and Draco hook-up. If J.K. Rowling had ever wanted to create a little fling between Hermione and Draco in her HARRY POTTER books, I guarantee this wouldn't have hurt her book sales.
I'm not against good girl/bad boy love stories. But the one good girl/bad boy story I've seen repeatedly in books and in movies that really irks me is the one where the good girl "heals" the bad boy by guiding him to be a "better" person, and then she dies, usually from a terminal illness or something no one saw coming. I believe writers go this route when they figure the good girl/bad boy romance would easily wither away if their characters had the chance to be together indefinitely. So why not just kill someone off, and have audiences mourn for a love that could've been, as opposed to showing an opposites attract hook-up that would run its course, and then get boring?
While I can certainly see the appeal of a bad boy, I also root for nice guys. Case in point: On Gossip Girl, a TV show based on a YA book series, I feel strongly Blair should end up with good-natured Dan over the menacing Chuck. While Chuck can be dark and intense, he cannot provide Blair with the emotionally stable relationship that Dan can. Besides, how many of you can trust someone again after they offer you up to have sex with their uncle as part of a business transaction?
Nice guys don't have to finish last. Second case in point: A Hermione and Draco flirtation might've have been fun, but Hermione will be much safer, better appreciated, and happier with Ron. Besides, I don't anticipate Hermione getting along with Draco's pure-blood parents very well.
Ladies and gents, do you cheer for the bad boys or the nice guys?