I think it’s fine if people believe in ghosts and spiritual stuff. My wife believes in ghosts, genuinely and fervently. I don’t really care to battle her on this because regardless of what she believes and what I believe we ultimately end up doing the same thing in the end - nothing. I think it’s a bit childish, but it’s no more or less unreasonable than faith in a god or a higher power and people will fight you over that.

I think the delineating factor is how much belief in ghosts or the supernatural play into your decision making and your worldview.

If a person believes ghosts are real, but never really act on that belief, it’s harmless.

if a person believes ghosts are real and alter their behavior in meaningful ways as a result, it’s maladaptive.

For example, say you hear a creaking noise in the middle of the night that startles you awake. Person A, Person B and Person C each check to ensure there’s no intruder in the house and determine that all the doors and windows are still locked and there are no signs of forced entry.

Person A comes to the conclusion that it was just the sound of the wood joists expanding or contracting as the temperature fluctuates and goes back to bed.

Person B comes to the conclusion that the sound could have only been produced by a ghost and therefore their house must be haunted, and so they call an emergency priest to come exorcise the house with holy water and they stay up all night clutching charms and wards to fend off spirits.

Person C comes to the conclusion that the sound could have only been produced by a ghost, says a quick (10 second) prayer for protection/guidance for the lost spirit and then goes back to sleep.

You can see how Person A and Person C have conflicting views about the origin of the sound, one which relates to scientific explanations for real phenomena and the other that delves into spirituality and faith to explain it. Regardless, they are both able to resume their normal behaviors (sleeping) afterward, while Person B shares the same view of the origin of the sound as person C, but their view is extremely disruptive and illogical. Their belief in ghosts requires them to take extreme measures to feel protected against them, but there is no evidence that anything bad would have happened as a result if they had chosen to do nothing instead. Nor would there have been a guarantee that something bad would not have happened anyway if they did all of the “proper” things to remain safe from ghosts.