I do believe in spiritual and supernatural phenomena that can't be explained away with natural laws, however, if a person was an atheist, would they discount that? I think people create their own realities based on their particular view of the world around them.
This has nothing to do with "demons" because I think demons via the JW religion are more of a fear/scare tactic. However, I do believe just like their are positive forces in this universe, there are negative ones and I have seen that manifest to not discount it.