I recommend anyone who is interested in this topic to check out Joseph C. Stewart’s book Demons: A Secular Look. Dr. Richard Gallagher’s book Demonic Foes is also a decent read, though it is more or less from an open-minded and modern Catholic perspective, albeit with a lot of psychological insight. In short, yes, these other-worldly “influences” are real, and have been documented over centuries, however, they are quite rare in terms of “possession.” Very rare in fact. Most cases happen because someone unknowingly messed with arcane or occult knowledge and made themselves ‘noticed’ and become targets of “oppression.” Some people deliberately seek them out, of course, and are unable to live with the consequences. Others are targeted simply because they are really “good” and pious people (no joke—the Church even has a name for this.) Very rarely do full-blown possessions happen. Why? Well, we simply have a built-in mechanism to fight off these invasive parasites, whether is our sheer willpower, mental strength or sustained belief in a much-higher deity or spiritual power. When we lack any of these things, we become vulnerable to “attack”. It’s undoubtedly a strange and weird thing to consider in our secular age—but to assume they are simply products of ignorance and superstition is to really deny the documented reality behind it all. I will add, though, the keeping people “scared” of these things certainly helps the Church advertise its business…so there’s that side of it, which in terms of the Catholic Church means classifying everything non-Catholic as demonic (“Oh my gosh is that a Buddha statue?!! DEMONIC!” “A Krishna votive? That’s demonic! “ And so on …) I would say that this attitude only hurts people who may want to know more about the underlying causes and various nuances of the phenomena.