Consider the following analogy:
A murder has been committed. There's a dead body, a broken door lock, a bloody knife, some finger prints, foot prints, and some scrapings of skin near the victim. Two detectives arrive on the scene. After examining the evidence they each reach two different conclusions. The first detective concludes that someone broke in, perhaps trying to steal something, fought with the victim, and ended up stabbing them and leaving in a hurry, leaving the knife at the scene. The second detective draws a different conclusion. He concludes that an evil demon appeared and killed the victim in such a way to make it only look as if it was a random murder, and carefully planted the evidence there to deliberately fool anyone investigating the situation. The second detective doesn't even think they should conduct an investigation, since he's already convinced it was a demon, and thinks any further investigation would be futile. The first detective thinks it's ludicrous to assume that a demon did it, and wants to immediately run the evidence into the criminal database for matches and have neighbors interviewed as possible eyewitnesses. Same evidence, two radically different conclusions.
They both begin to argue. The second detective accuses the first detective of presupposing that demons don't exist and can't be responsible for the murder. The first detective says that there's simply no evidence to draw the conclusion that a demon is the culprit, especially when there's finger prints, a broken lock, foot prints and a bloody knife. And he adds that the demon hypotheses has never worked in the past. Not once. Every solved crime has always had a human culprit. But the second detective argues that they cannot rule the demon hypothesis out, since it could be true, and as long as it's even a possibility, it should be considered valid. The first detective looks up and sighs.
How you ever felt like the first detective when arguing over god and religion with a theist? I certainly have. There are some theists who think that demons haunt our world and that even though we have natural explanations to suffice, they'll say that demons use those natural forces to achieve their goals. They will freely admit that there is no physical evidence for demons at all, but that the natural causes of events like lightning, earthquakes, diseases are secondary causes and not primary causes.
But think about this: Demons are intentional agents, they have a will. They desire evil and suffering in the world. So why is it then that their will always seems to fall within the confines of the natural, predictable laws of physics and biology? I mean, wouldn't the demons be able to violate the laws of physics since they're supernatural? Wouldn't they be able to affect the natural world in a way that is obvious that some kind of supernatural intelligence is behind it? Why spread diseases mostly in third world countries to poor people whom we'd expect to have those diseases? And why should their attempts to use diseases to cause evil be routinely thwarted by our medical advances? Why would they only cause earthquakes along fault lines of the earth's tectonics plates exactly where we'd predict they occur naturally? Why cause hurricanes only in hurricane zones? Why not cause all of these disasters randomly and unpredictably around the world as our superstitious ancestors once believed? It just doesn't make sense to believe that demons cause anything in our world.
If there's no distinguishable difference between the natural world and demon haunted world, then isn't it reasonable to say that the demons are all in the heads of their believers, especially when we know how imaginative the human mind is? I don't see at all how it is objectionable or dishonest to conclude that something that leaves no trace of evidence whatsoever, doesn't exist. The theists can believe in their demons if they want, just don't force me to acknowledge them or teach them in public schools, and don't craft public policy based on those beliefs.
In other words, keep your demons to your self.