What modern audiences, living sheltered lives, preoccupied with escapist entertainment, and only capable of relieving boredom through sexuality and the grotesque, fail to understand about the origins of both the werewolf and vampire myths is that these were never projections of desire but of fear.
When werewolves and vampires were truly believed in, there was nothing seductive about them. They were seen as monsters, plain and simple. And this went unabated for centuries. It has only been recently–due to both cultural changes and the advent of science–that the old fears that this monsters represented have diminished. Take the werewolf, for example; in the earliest myths–before the devil got involved–they represented three powerful fears that have plagued humanity from the very beginning: cannibalism, losing control and hurting loved ones, and possession by demonic forces. These fears are what gave birth to the werewolf legend.
By the time human beings had become civilized–organized in a socially complex way, with a uniformed belief system and value system, and a sustainable way of life–cannibalism had become something abhorrent, something that could no longer be understood save by positing that a human being had become an animal. It is interesting to note that the oldest werewolf story we have–by the Roman poet, Ovid–is about a cannibal king–Lycaon, from whom we get the word Lyncanthrope–punished by Jupiter into becoming a wolf for his abominable appetites. It is also interesting to note that were-people are always dangerous animals and not bunny rabbits.
Now, as to the fear of losing control, an argument can be made that the werewolf myth–or any shape shifting myth that involved a dangerous animal–is a primitive explanation for rabies and madness. Losing control and hurting the people you love can be quite a traumatic experience, and in primitive times, where people ate moldy food or questionable mushrooms that could have triggered a hallucinogenic episode that left its victim behaving like a wild animal, a very real fear.
Finally, possession by demonic forces was a very real fear in the ancient–and not so ancient–world. While this notion may seem laughable to many today, it was in the past feared more than death. Demons were used to explain famine, disease, plague, and disaster; they were also used to explain unusually wicked behavior. A demon possessing a man, even if he were a good man, would turn him into an unspeakable fiend capable only of causing suffering and misery.
Before I end this, allow me to touch upon the vampire myth. Vampire myths are not as complex as werewolf myths. While the evolution of the werewolf myth passed through many varied stages (it was used to explain cannibalism, what we would today call serial killers, madness, rabies, and particularly ferocious enemies that happened to dress in animal skins, e.g., Berserkers) the vampire myth has always been about death. In its earliest manifestation–the Lamatsu myth–the vampire is used to explain the deaths of infants. Later, also in different cultures, the vampire became associated with other types of deaths–stillborn infants, victims of bubonic plague, etc. The fear of vampires grew so great at times that the recently dead were sometimes pulled out of their graves, decapitated, and had their mouths stuffed with garlic before being reburied. Fear of death was manifested as fear of the dead, fear that the dead, still craving life, would rise and drain life from the living.
In conclusion, the modern phenomenon of the sexy vampire and the sexy werewolf (necrophilia and bestiality) is something completely modern, a product mostly of Hollywood and of escapist literature, bearing no relation to what people actually believed when they thought these monsters real.