Alycone wrote: Religious and other moral decisions aside, we need animals. As food. How can we be certain a human only diet isn't the best course for a vampire?
This is an interesting thought. However, in terms of the books, I don't know that there's anything to back this up. The Cullens seem just as strong, if not stronger, than the rest of the vampires. Strong both physically and mentally. I would even consider them mentally stronger than those around them. It has even been insinuated by the other vampires (Garrett?) that the possible reason for them to coexist in such a close family bonded group is because of their lifestyle and food choice. Yes, the Volturi live in a group, but I don't know how bonded they are as a whole.
December wrote: So yes, it makes sense that the average newborn vampire is wild to relieve the remnants of the pain they've endured for three days; but this mightn't be enough on its own to carry them the full distance from humanity to ruthless predator, if it weren't repeated, unrelentingly, for a very long time....
I would have to agree with this point. I think there is a combination of factors that distances the newborn from humanity, the newly found thirst being a possible factor as well as the pain that some of you noted. Pain definitely makes you capable of crazy things. As Alcyone pointed out, if you've ever been in intense pain before you realize that you're acting like someone that no longer resembles yourself. However, when the pain is over, most people are capable of going back to their normal selves. But for vampires, a small remnant of that pain carries on. I can see the first instinct being to quelch the last of the pain. But like December says, it's the continued cycle of this that slowly creates the divide between the current self and the former self.
I also think relationships have a big part to play in this distance. The Cullens have managed to retain a great deal of their humanity, as seen in the respect that they share for human life. (Yes, I know some of them have slipped up, I'll get to that in a minute

) They have emotional bonds to
several of their own kind. They have a reason to
choose to stay connected to their own humanity because they see it modeled in their father/leader. So, partly, I believe it is a choice to stay connected to one's humanity, if given enough reason to do so.
Secondly, I posted this on the TUGPM thread. I believe that the state of the person prior to transformation also plays a key role in at least the ease of retaining humanity. When I say this, I'm thinking of Bella. Before she was transformed, she had everything that she desired and even a little bit more than she had realized she desired. At the point of her transformation, she was whole. Her human life was fairly complete and satisfying for, satisfying probably being the most powerful her. So, when she turned to her vampire self, she was left with no unfinished business from her former life, so to speak.
She was already satisfied. So, she didn't need human blood to satisfy any holes that were left from her human life. Thus, her thirst was managable.