Spoilers ahead, of course.
Am I implying that the evilest of creatures in the Ponyverse is...MAN?
That's right, the Pony Conversion bureau fanfics were correct. Ponies are superior to us in every conceivable way.
In the Ponyverse, the Element of Magic cannot work without the other Elements because it is based on dependence on friends. In the human world, it not only works regardless of any other Elements (proof that humans are selfish beings who only depend on themselves) but turns lone human wielders into demonic monsters. It's implied this is so not because Sunset is a powerful unicorn in her homeworld, but because the human world has corrupted the element.
When the Elements DO work properly, they cannot process that humans could POSSIBLY use it for harmonious purposes. So they partially convert the wielder into a pony so that "True" harmony can be restored.
Final proof can be seen when the Human Six have NO PROBLEMS WHATSOEVER with being turned into anthropomorphic pony abominations, complete with horse ears, and when Pinkie tries escaping the hell that is the human world with Twilight.