1. Discernment of Good and Evil
Since the dawn of time mystics and religious leaders have tried to discern what types of spirits are behind the events of the world. Importantly, were they good spirits or evil ones? "In traditional religions" shamans and the like would have the important duty of contacting spirits and finding out if they were benevolent or malevolent1.
Throughout the middle ages priests would bring in revenue doing exactly the same thing. New Agers and modern mystics pride themselves on how they can "feel" if a spirit in a particular room or location is good or evil, helpful or harmful.
2. Free Will
It holds that if we have free will to choose our actions whilst alive, and that our life comes from our soul, then our soul is what has free will. Our bodies are just biochemical machines; those who believe in free will and souls no doubt hold that it is the soul that allows free will to be exerted upon our otherwise mindless bodies. As the source of free will, the soul must also have free will after bodily death.
This means that you cannot have spirits that are good or evil: They are capable of free will just as any other higher life. To say that a spirit is "evil" or "harmful" or "bad" is saying that it has no free will to act haphazardly. Although some humans seem to be almost purely evil, and some humans almost always attempt to do good, the vast majority exist in the middle ground. Spirits, at least the ones that are departed humans, continue to have free will and no doubt continue to mostly occupy the middle ground, being sometimes good, sometimes bad.
We all know that the most ill-seeming men can sometimes be the goodguys and that the most openly kind can frequently be the most callous and secretly evil. This brings to mind 2 Corinthians 11:14, "And no wonder, for Satan himself masquerades as an angel of light". If the most evil beings can fool puny Human minds into appearing good, then, what chance has anyone of truly deciding if a spirit is good or bad?
3. Psychology
Certain rooms, atmospheres are locations lend themselves to a general spookiness. A sense of malaise. This has been studied extensively not only by occult, new age and magical practitioners but also by sociologists and psychologists. It is surely the case that we are only reacting to the environment. Anton LaVey, founder and High Priest of the Church of Satan from 1966 until 1997, held the belief that various factors would determine whether people took kindly to a location or not. Odd angles, smells that are just-below-the senses and breezes, the quality of the air and various other things could all conspire to make people feel unease. This would of course lead to certain places becoming associated with evil spirits. More mainstream psychologists have put forward multiple and varied descriptions of how the subconscious can lead to feelings of being watched, of "presences" of either good or evil spirits. But above all the Human nack of over-simplification and over-confidence that is the final obstacle in realizing the true nature of spirits: neither good nor evil, but gray, just like free willed Human beings and animals.
Fear and emotions generate either bad or good experience of "spirits", the phenomenon is subconsciously self-created, this is also the conclusion of a good study of supernatural events and the human subconscious, "The Origins of Psychic Phenomena: Poltergeists, Incubi, Succubi, and the Unconscious Mind" by Stan Gooch (2007) [Book Review].
4. Conclusion
The Human subconscious and environmental factors determine if we find a particular place spooky or whether we think a good or evil spirit might reside there. Most the time it is human projection. But given the existence of free will it seems that no spirit is either "good" or "evil": They will sometimes be good, sometimes be evil, just like Human beings. In addition, evil spirits can trick us into thinking they are good spirits, and sometimes even the most kind and benevolent person simply comes across as nasty (like God in the Old Testament): It is dangerous and wrong to pronounce that spirits are "good" or "evil", benevolent or malevolent.
