Possession of a demon/s is evil because the demon is evil and a possession that is unwelcomed is evil because it is disrespecting the body of a person. When Jesus manifest Himself in a priest this is a form of possession but it is holy because it is Jesus and it is also a welcomed possession. We also say that our bodies are temples of the Holy Spirit, the Holy Spirit is in us and it is welcomed.
I was just reading an interview of the exorcist Father Amorph and he says that he has encountered demons pretending to be souls. But, there are exorcists that say they have encountered actual soul possessing. Amorph thinks that the jury is out and it is a job for the theologians to look into the matter of life after death.
I Googled the topic in french because a french exorcist is quoted in a book who states he has experienced souls possessing and wanted to learn more. I came upon a french Catholic forum where people have discussed and explored this topic and with no aggression. Even a priest participated in the discussion. There they bring up Pope Benedict’s Spe Salvi 47 where he states that we do not know how long the
passage of death takes. And of course, they quote the theologian and exorcist Padre Fortea.
docteurangelique.forumactif.com/t9283-des-exorcistes-confirment-l-existence-des-ames-errantes
The jury is out on human souls possessing be they from hell or purgatory; but, those from purgatory or heaven appearing although not declared in a council is accepted by the Church. It’s true that the faithful are not obliged to believe private revelations, Lourdes, Fatima, Padre Pio, Saint Faustina etc… but, in my ignorance and all; I consider one of the steps to canonization is to be given a nihil obstat. Meaning that what the person has said (e.g. Padre Pio and Saint Faustina) is not against the teachings of the Catholic Church. Certainly, a heretic would not be canonized. But, what have Padre Pio and Saint Faustina shared regarding the souls in purgatory? They have both stated that souls from purgatory have appeared and spoken with them. So, indirectly, we know that souls appearing is not against the teachings of the Church and is not in conflict with the teaching that souls are judged after death. How do we make sense of this apparent conflict? This is why people wonder how long the passage of death takes, that journey for which we take the viaticum.
I think that when a person approaches a priest to tell him a recently deceased person appeared the thing to do is to recommend a Mass be given. Not to deny such a thing could happen. I don’t think this is controversial and should be taught in seminaries. Now, regarding possession of souls from hell or purgatory - the Church needs to look into it and is. Insofar as to the possession I witnessed, two of the spirits seemed to me to be human souls but, spiritually it is not as though I could make a clear distinction. Firstly, I have nothing to compare it to, I have not had the experience of a possession by exclusive demons to compare it to but, most of all I could only sense so much because of their coldness and their condition but two of them did appeared to me to be human souls this is the reason I started my little research.