The general stance of the site is that these things are "fluffy" fantasy. These things simply do not exist within the physical world.
Vampires, while originating within folklore of a wide range of cultures (most frequently as spiritual entities that feed on your life essence - not unlike many relatively common spirits), evolved within their mythology into the more complicated concepts that we see evolving up until the common Bram Stoker version of the vampire and the modern variations. Almost all discussion of "vampires" on this site refers to these modern concepts that have no basis in any sort of lore or reality. Even those concepts that do have some basis within truth are rooted in a misunderstanding of illness, the decomposition of bodies, and similar circumstances that left our ancestors scared and superstitious.
There is the "psi vampire" as well, but this is, in my opinion, an individual who through some emotional/mental trauma has become dependent on draining energy from others. They often view this act as a necessary thing for their continued well being. To my experience, resolution of this trauma also results in any sort of "necessity" disappearing.
Werewolves, similarly, have a great deal of lore throughout history. They are rather easily explained however, once one considers the ancient and medieval lack of understanding of diseases that can cause violent, raging psychosis and wild behavior. Imagine that a man in a medieval village gets bit by a rabid wolf. The wolf is killed, but some time later - perhaps a month, when the moon is within Full phase of its cycle - the man starts foaming at the mouth, growling, biting, clawing, and otherwise attacking all who come near him. This could very easily be construed as some sort of magical affliction. It is, however, just Rabies. Other diseases and disorders can also quite readily contribute to this myth.
So that leaves us with what? Hollywood fantasy and the individuals too bored with their own likes to give up on the possibility that what they imagine may, in fact, be real.
Well, it isn't. End of story. Case closed. And when it's pushed in the chatter I gag for roleplay.