>Nobody was claiming this is true for infants or small children, too, and I am a mature adult.

I was providing evidence that because this fear does not exist in infants, it is not innate. It is learned. If it was innate, infants would also be scared.

>I absolutely cannot imagine fearing a vampire when looking down a dark alleyway

I find it extremely funny how literal you took this. The fear of the unknown is that feeling we get when we don't know. For example being in the middle of a forest at night, not knowing what those sounds are or if people are around. Alternatively, that terror we feel when we see images of the deep dark ocean. This fear of the unknown is what fuels our other fears. Such as social anxiety, we fear the social interaction because we do not know what is going to happen, only that our mind starts racing to worst potentials.

Hope that explains it in a way you can understand. Avoiding mention of vampires because I don't think the fictional creatures helps grasp the concept of the unknown.