The first double-spirited men -- now known as vampires -- were created by kabalistic magicians during the inquisition as a means to fight the inquisitors. Although they had to act in secret, their fight was largely successful. The fact that vampires were originally created to fight a corrupted church also explains why vampires are so easily upset by the appearance of crosses.Now, if only he can show us some real vampires. That would be great!
The reason that vampires now have such a bad rep is that if the magic that binds their second spirit to them is not periodically renewed, their mind begins to age, even though their body remains young forever. This leads to a specific kind of madness, often expressed in unnatural desires (e.g. for blood). Fortunately, someone with experience in the particular kind of kabalistic magic needed to create a vampire can restore a vampire to sanity. If we could encourage this, vampires would once again be a force for good.
Update: For real blood sucking action, take a look at this National Geographic video showing "vampire birds" in action.