What if we are supposed to live without causing suffering and pain..... to anything with nerves to feel it and a brain to understand it! What if meat is actually the "forbidden fruit". Do you know enough sources to get your proteins, aminos, and nutrients somewhere else without killing?
Maybe the idea of vampires comes from people drinking blood of animals/beings that died during an adrenaline rush.
Or maybe the idea of vampires comes from the idea there are extraterrestrials and they scare us into having an adrenaline rush and they drink our blood...? Hmmm, I don't know but there is always a reason and partial truth to the beginning of every myth.