Why couldn't you study a group of self proclaimed vampires when you can study other groups of individuals? What would make studying their lifestyles any differently.
This is coming from a standpoint of identity. Similar to transgender people wanting to be called a man or a woman and having rights.
If someone wishes to believe that they are a vampire should we deny them that?
I guess it could be compared to someone's right to believe that Jesus is the son of god. Not a drop of science could support that. But people can freely claim that it is true, that they partook of his blood and his body, and that they are on their path to joining him in heaven.
No science can prove who is god or if there is one. Science shows nothing about star signs, or daemons, or mother goddesses, or the power of gemstones.
Just like no science can prove a person is a vampire. It's fairly easy to prove that they are not. But then again, by the same standards most if not all of this sites discourse would also be proven to be just superstitions.