The point is not whether they do exist, or someone believes they exist, the point is whether the belief itself is compatible with the mainstream Christian beliefs of heaven and hell. It isn't.
BTW Purgatory isn't ghosts haunting a house, it's more like "hell lite":
"Pain and fire
Purgatory is a cleansing that involves painful temporal punishment, associated with the idea of fire such as is associated with the idea of the eternal punishment of hell.
[31] Several
Church Fathers regarded
1 Corinthians 3:10-15 as evidence for the existence of an intermediate state in which the dross of lighter transgressions will be burnt away, and the soul thus purified will be saved.
[31] Fire was the Bible-inspired image ("We went through fire and through water")
[32] that Christians used for the notion of after-life purification"
And more to the point:
"In 1999
Pope John Paul II declared that the term Purgatory does not indicate a place, but "a condition of existence".
[16]"
which goes against the notion that purgatory could be human spirits residing on earth.
:sleep: