Those absolutist statements are in reference to the Cullen's, since they're the vampires that the reader really gets to know. Yeah, I know the Volturi and pretty much all the other vampires are evil. But the Cullen's are the main characters.
Realistically, main characters should have flaws. It's what makes them relatable. It doesn't matter if the main character is a vampire or not, they need flaws. In this case, with the vampires, it's okay to mess around with the folklore, but you really have to be careful with it. I even think it's okay to take out the human-bloodsucker aspect by making them veggie vampires, but if an author does that like Smeyer did, they NEED to give the vampires a flaw .
Resisting the urge to suck blood is not a flaw. It could be considered a flaw, if one of them gave into the impulse. But none of them do. I'm not saying one of them needed to give in, but a flaw would've been nice. Even if that flaw was some explained backfire of drinking the blood of animals in replacement of human blood (and not that animal blood isn't as potent as human...something else).
I can't think of a single flaw in the Cullens. They're perfect. And that's distinctly unrealistic. Yes, they're vampires. I know. Vampires are unrealistic. But they're the main characters. They need to be relatable. No one is perfect. Not even supposedly perfect vampires.