For why vampirism as the norm would be a terrible idea, see the film 'Daybreakers'. There wouldn't be enough blood to go around. Also, the more people you drain blood from, the more likely you are to get caught. Every drainee you leave alive is another person who knows what you look like and can report you to the authorities.
Anywho, between Jehovah's Witnesses and vampires at my door, I've got to say I'd rather have a Jehovah's Witness. In my experience they can actually be really good for a chat, they leave if you say you're not interested, and they don't try to kill you and/or suck your blood. In fact, I'm fairly sure they'd turn down your blood even if you offered it and they needed it (no blood transfusions IS one of their things, right?). Oooo, imagine what a hard time a Jehovah's Witness would have if they were turned into a vampire!