Ghosts are comprised of energy. YES, they exist, and they have less to do with God or the Devil, and more to do with people without bodies.
Ghosts are simply a residual form of self imprinted on the energy grid we use/call EMF (electro magnetic field). While the physical body no long exists, the residual self can/does. This is why you (animals) can "sense" them when they are around. This is why machines like, recorders, cameras, FLIR, KII meters, and other energy collection devises pick up their voice/image.
Good vs Bad Ghosts. Just as their are good and bad people walking around the earth, there are good and bad ghosts. Born with an innate "knowing" and "mediumship" ability, ghosts have/are always around me. Born and raised in a bizarre religion, it was very confusing for me to navigate through life when my crazy parents would tell me these beings without bodies are all demons
. As I got older I learned how to manage through these encounters through many spiritual groups--this really saved me from mental disasters throughout my life.
Working with the paranormal I feel I have a more positive outlook on ghosts/spirits in general--they are just people without bodies, and that is neither a good thing or bad thing--its just the way of it. Don't let God or the Devil become the goalies.