I am not a traditional anything, but the usefulness of the concept of "demon" - as the personification of a vice, or misfortune, or cultural problem, or even mental illness - is shown I think by its durability across traditions as a useful explanatory model (and a metaphor.) They exist like an uncollapsed wave function - you will never meet one, so the validity of its existence" is always somewhat unclear, but it can be very useful to act as if it is quite real.