So in the past a study on infants might claim that with seeing spiders they show fear, but modern studies only demonstrate infants show increased alertness. Contrasted with adults/older kids where this fear shows up as we expect in brain scans and behaviors. Basically, it's a learned fear, and is also why we don't see other animals in the same way when logically we should.
The fundamental fear of the unknown makes more sense as a source, in which the fear of demons or vampires becomes understandable when they were created to creatively prey on the unknown. Eg. vampires lurking in the shadows/night. This fear of the unknown can also explain why exposure therapy can be so effective, you're filling that void with knowledge.
This fear of the unknown would also explain why new modern creature creations can be scary, despite quite literally knowing they cannot physically exist, we still have that little bit of our amygdala going "but what if we don't know..."