Completely avoiding all the wank elsewhere, and disclaiming that I've only read so far in the first book of Twilight and the rest I've gotten through summaries:

My problem with the series isn't that it's a fantasy, or a dark fantasy, or that it conveys some unhealthy behavior. I read and roleplay that all the time, I've always wanted to indulge in or at least laugh at some bodice-rippers. If you want to talk about bad influences, I watched South Park at age 12 and came away with little more than a filthy mouth and an advanced interest in politics just in time for the Bush administration. But none of what I've read, written, or watched has ever said 'this is the ideal to strive for,' not even Grand Theft Auto. And I look at the response to Twilight - not just the books in of themselves, but also the response - and see that the author AND a lot of the audience genuinely believe that these are expressions of true love. In reality. Without exception. If you try to suggest it otherwise, they will get furiously angry, they will draw back as if scalded or (I've heard this anecdotally) key your car.

I don't like the 'it sucks because it's popular' tack, but in this case I think it's what influences the concern. Twilight creates this mania that other romances haven't created since...basically ever. Lines a mile deep and near-rioting teenagers and people asking RPattz to bite them. Grown women who stalk the set and are encouraged to use a fictional character's engagement ring to show they're married. And everyone talking like it is the greatest work of literature to ever grace the universe. I have never seen a weirder response to a fandom. I remember being a young teen and feeling like everything was a matter of life or death, but I was never THAT emotionally volatile about it.

You're framing a lot as taste, from what I can tell, but I'm talking about people who say 'I want an Edward of my own.' It's not just teenagers, there's a lot of grown adults that think this is a sincere love story too. And I watch Edward's actions and think 'every single thing this person does is, down to the wording, the sign of someone who will be an abuser later in the relationship.' No, I don't think Twilight IS the problem, it's a symptom, but the symptoms can help define the problem sometimes. How do we judge history? From primary sources. We mock the 50s domestic ideal through its advertisements, and so on. And unchecked ('checked' meaning talking and analyzing and educating as to fantasy vs. reality), media still stirs up and influences - not necessarily in big actions, like everyone's going to throw themselves off a cliff after a breakup, but in things like people's instincts. If things like rape and suicide and spousal abuse weren't still a big problem due to people NOT being educated about their warning signs, I wouldn't be so worried.