Owlswing. OP title: Which century are we in?
Do you really think that because we are living in the 21st century, the spiritual realm has ceased to exist?
Exorcism was, in the 15th century, the sole prerogative of the Catholic Church, The use of the rite declined almost to extinction over the next five centuries, but revived with various films, including but not llimited to, the Exorcist films.
The idea of demonic possession is now almost totally restricted to the adherents of Voodoo and Christianity, particularly the Catholic church.
The existence of, and use for negative purposes of, demons are also one of the favourite claims made in attempts to "demonise" pagans and witches, frequently evidenced by posters on this forum when attacking my personal beliefs.
Of course the spiritual world still exists, it is the use of negatives attributed to that world and created for the purposes of allowing priests of Christianity to claim curative powers relating to (probable) mental conditions and expertise that they do not possess that I object to.