I agree for the same reasons you state here. Spirits are allowed to manifest even if they have gone to heaven or no-one could have ever have seen a Saint, Blessed Virgin Mother Mary, St Therese etc.
I think there are two reasons people believe they experience ghosts, because I don’t believe ghosts exist. Firstly they are simply evil spirits or secondly it may be due to the fact of eternity, I don’t know how to propose this, but I’ll try, perhaps God allows time to be suspended in order that a person may see back into time or into the future as all eternity exists in the eternal moment and therefore ‘person/s’ appear to manifest, but still this would be a spirit .
In any case keep well away from that stuff!