BlueOrchid wrote:... I realized if the situation had been anything but life or death, Edward would always feel guilty for "killing" Bella.
That's interesting! I hadn't thought of that. I have another possible reason:
Stephenie has kept on reminding us throughout the first three books that being a vampire is a huge sacrifice. The Cullens certainly make us like vampires more, and Bella can think of nothing else but joining Edward as a vampire, perhaps the reader sometimes forgets what she might be risking. I think Stephenie had to write a mildly horrific scene to hammer home the full meaning of what Bella has done by giving up her human life. Is she playing with her soul? In any case, it makes us think twice about her decision.