This discussion, i feel, only proves the disparate disconnect between a 'concept' (existence of demons) and an absolute (cold, hard, 'palpable' evidence that CANNOT be refuted or denied by any intelligent and reasonable human mind).
it could be akin to once attempting to prove that the sun (or earth) was/wasn't the center of the universe, and eventually man accepted whatever proof or evidence of it became recorded.
will we one day have absolute proof of the existence of demons? hard to say. we have so far so much evidence of so many other once 'inconceivable' claims, why is this not the case with demons?
there is still a small (very small) part in my brain that says there is a chance, but its becoming reduced more and more.
man can be 'demonic' (murdering, hateful, abusive) there is plenty of proof of that.