I don't like Renesmee, or even Vampire Bella, either. Renesmee is a plot device (Cullens and mga lobo are allies in essence because of the imprint, etc.) and Bella's perfect control of her thirst, skipping the rabid newborn stage, being "graceful, even for a vampire", and pangkalahatang being perfect in her unlife annoys me and makes me roll my eyes.
But Meyer has already created them, they've already been established. So there's really nothing I or anyone else could say or do in to make them "disappear". My biggest problems with Twilight mostly appear in Breaking Dawn, and just because I can see its faults doesn't mean I hate it. I obviously enjoy it, or else I wouldn't have a Dedicated in this spot.
No, I like Nessie's existence. There was madami to having her in the story than creating a situation where Bella's vampiric transformation would effectively save her life. For one, giving them a child they'd believed was impossible perfects the happy ending. It also finishes off the pag-ibig tatsulok story. And obviously you needed someone to be mistaken for an immortal child or you'd need another excuse for the Volturi to attack.