Here is yet another crackpot theory about this train wreck of a fanfic, because I haven't got anything better to do: Snap is the true villain of My Immortal, who, as a fundamentalist Christian, tries to destroy everything related to goffikness.
In chapter 38, James tried to kill Lucian, which ultimately is revealed to be because Snap possessed him. During this time, Tom Satan Bombodil is still a goff, meaning he could not have commanded Snap to do so. It is explicitly said in the fic itself he only turned into the Bark Lord Volzemort because he suffered a borken hearth. Since Tom still wasn't Voldemort, he was still goffik. This means Snap possessed James on his own accord. This also means Snap acted against goffik people before Voldemort founded da Death Deelers.
In the author's note of chapter 9, it is said Snap hates Harry 'Vampire' Potter because he is Christian, while the latter is Satanist. In chapter 11, Snap seems to fear Hargrid after the little Hogwarts student loudly proclaimed to be a Satanist. When Hargrid tries to tell why he is a Satanist, Snap fearfully guesses it is because Hargrid is Goffik, meaning Snap (correctly) links goffikness to Satanism.
Since Snap is established to be Christian and, chronologically, the first person to act antagonistically towards goffik people, it can be assumed he is acting in a bid to destroy all goffs in order to protect the world from their foul Satanic grip. To do so, Snap first tries to destroy the band XBlakXTearX from the inside, by possessing James. After that, he causes Tom Satan Bombodil to suffer a borken hearth which turns him into the Bark Lord of the preps Volzemort. With such a powerful wizard becoming a prep, Snap is one step closer to victory. After Voldemort subsequently creates da Death Deelers, Snap quickly joins and tries to use Voldemort's powerbase to destroy all the goffs.
Unfortunately for him, he and his efforts are no match for Ebony and her terrible Mary Sue powers. No matter how devout one is as a Christina, no one stands a chance against a Mary Sue and her reality warping nature...