I agree with Monsieur in that this seems to be a subject where direct personal experience appears to offer the most convincing type of evidence. Such experiences are usually not themselves convincing to others. This is particularly so where one doesn't know the person reporting the experience.
To assert that there is no evidence at all of supernatural phenomena is, IMHO, incorrect. For the interested, a good place to start is David Fontana's "Is There An Afterlife". Although I would not expect a rational person to read this and emerge fully convinced (as I did not), I do think it is unreasonable to look at even this subset of the evidence and dismiss it out of hand.
Accepting for a moment that such phenomena occur, the term 'demonic' carries unnecessary religious overtones as far as I an see. As far as the topic is concerned, it depends on what one terms as demonic. Is all purported communication demonic or just the ones that frighten us?
The assertion that many communications that are said to originate from some 'spirit realm' contain urging to kill or hurt others is untrue. The vast majority of such communications, if such they are, are perfectly benign.