If there actually WERE vampires, and someone DID have the power to destroy them, the destroying of them would be a lot less of a cause for trouble, than them just being allowed to go on scarfing on people.
I would LOVE to enter the Twilight reality AS Grey Eagle, stroll in on the Volturi, hold them helpless with my telekinesis, and tell them, "YOU are all done snacking on tourists!"--then send them all to H-ll.