Remember your childhood and the fears that plagued you. A dark bedroom may as well have been the den of a wild animal, or worse. The creatures that dwelt there took on the shape of the darkness in which they hid. And such patience! In a closet or amid the dust-bunnies under your bed, whatever it was could wait forever. A naked foot reaching to find the floor for a late night bathroom visit could deliver you to a horrible fate.
We didn't consider motive. Not for long, anyway. The denizens of the gloom existed to snatch you from the safety and comfort of your home, from the unconditional love of mom and dad. It didn't matter that you had never before experienced anything resembling evil; hatred, intolerance & cruelty, perhaps. You had your imagination, and that was enough. Unlucky children were seized and taken somewhere (and what a big world to hide in!) and cooked, eaten, tortured, smoked and skinned and worn, to the admiring growls and roars of the other things in the dark.
They all knew each other, and they all wanted you. These were taking things, not polite asking things.
But it didn't seem to matter what the monstrous brutes had in mind. At least not for me. What I feared above all was being away from my parents and my brother and sister. Into the world and away from my loving family. The people who seemed so powerful to my young eyes would be rendered impotent because I would be lost, out in the world somewhere. And as I said before, it was a very large world in which to be lost. Countless hiding places in which to be taken.
If we are lucky, and no real world horrors close our eyes forever (a cross town bus or a disease, perhaps), we get to grow up. We learn the names of the places in the world, and that makes it seem smaller. We meet people from distant places and realize that there are no monsters there, just people.
The diseases and injuries get names, too. The affect is calming. Even the aching enigma of mortality is alleviated somewhat by the commonality of experience with other humans, also seemingly cursed to comprehend their own small, ephemeral place in the universe. And what a universe in which to have a place! If we feared the dark places of our bedroom as children, we fear the dark places in the universe. As adults, however, we don't fear the monsters that might lurk there. What we fear is darkness with nothing lurking within at all. Just the dark.