Vampires are evil. It's easy to forget that simple fact, given the way modern culture looks at vampires:
Vampires aren't evil, they are cool!
They have sarcastic anti-hero personalities, and make witty quips while defying authority. They are super-sexy and seductive. They have super strength, and can fly, and make awesome boyfriends. They can have children, and they can half half-vampire children with mortals.
They're basically a race of superheroes, only they can't go in to the sunlight.
They aren't even necessarily undead, either. As mentioned, they can give birth to offspring. When I Am Legend (the book) first came out, it offered a new explanation in terms of a virus, and that has become the stock explanation of not only vampires, but zombies, too.
So it's easy to forget where they came from, and that is medieval notions of the antichrist.
Vampires are evil.
Not the cool, sexy evil. They are the horrifying, creepy, upsetting evil. You do not want to be a vampire, or know a vampire, or date a vampire, or have babies with a vampire.
I saw a vampire movie recently that, very subtly, I think showcased this more than anything else.