creepy

Well, taking ghosts, I don't think it likely that ectoplasmic echoes of the dead are spooping around - but if someone has a conversation with their dead friend one night, that isn't unreal just because it arose from their brain. Humans leave echoes of themselves in each other, and we animate them all the time without noticing, just in the course of our normal creation of our own perceived consciousness.

Following that, curses and symbols and suchlike might move through human populations and "spirits" give the appearance of having a person-like existence - we humans aren't singular things, our selfhood is bound into a web of interpersonal and environmental interactions, and fuzzy around the edges. So these mental vibes can transmit through that layer and result in behavioral effects in the humans they touch, and I don't think that's too different from having an Astral Plane or Underworld with gribblies and spirits. I doubt that rituals and such conducted in secret would be likely to manifest actual knock-on effects on the target, but if they alter the ritualists behavior (such as increasing their confidence or resolving some tension) then they still have an effect.

I don't particularly think it's worth trying to quantify though. I enjoy it when it seems appropriate, use its language when it has a better grasp on certain subtleties or just got there first (corporations as egregores, etc), and am sympathetic to it.

Plus, as another poster said, since there can be an underlying cause that created a supernatural explanation - such as mold, toxic air, poor construction, mosquitoes - that does generally suggest a level of respect is warranted case-by-case, much like how historic medicinal plants are valuable sources for investigation even if Lungwort probably isn't healthy because its leaves look like a lung.