To be fair, fear of demons was a cultural phenomenon in the U.S. in the early 60's. It seems to have been touched off by a 1959 book by a French Monsignor on the dangers of the spirit world and quickly crossed denominational lines and even found its way into pop-culture via movies like Rosemary's Baby.
Alleged demon / ghost / supernatural experiences were common fare even in the Reader's Digest at the time, so the JW's were not completely alone in this lunacy.