Demonic obsession gets mentioned a lot in this discussion. Well, I know a lot of people who are obsessed by the Holy Spirit - to the extent that the other day I had to deal with a DNS poisoning issue with this blog, which kept redirecting the URL to some evangelical ministries website, assumedly devised by some righteous holy hacker. I also had to deal with a spiritual attack from the self same bunch waged most likely with imprecatory prayer. Talk about obsession. Lord only knows why my little blog would provoke such an effort - I wasn't going to give them any air time, for fear of encouraging their bigoted shenanigans but it seems appropriate to mention. I am not going to even go into the religious nut-jobs who kill, beat and maim for Jesus. Is the Holy Spirit a corrosive, inhuman demon?This is a very interesting point. The atrocities committed in the name of Satan pale next to the death toll from people who killed, tortured and enslaved in the name of Christ. Is this the fault of the Holy Spirit and are these people suffering from spiritual obsession? Spiritual oppression leads to personality changes: so do many mystical experiences. And trying to sort out positive from negative personality changes is a tricky endeavor. Lots of martyrs were inspired by mystical experiences to go to the stake for their faith, and very few people would say that being burned alive is a positive life-change. What some may call devotion to a cause others may call brainwashing by a cult.
I suspect that many of these cases are not spiritual obsession, but rather psychological imbalance propping itself up with religion. If they weren't Hackers for Christ or Fag-Bashers for Jesus, they'd be using Karl Marx, Allah or some similar excuse for their misbehavior. But this of course begs the question: how many of the people who report "Goetic obsession" are merely suffering from a psychological imbalance triggered by the events which led them to resort to the Goetia?
Perhaps it would be helpful to draw a distinction between individuals who have sustained changes after an encounter with the spirit world and those who appear to be suffering continued oppression from a spirit entity. Divine encounters frequently result in changes in the mystic's life and outlook, but the entity in question doesn't stay around and micromanaging the mystic's consciousness. With spirit oppression, there's Something Else which steps in and starts reprogramming the person. In my experience, this Something Else is typically either a wandering ghost or a lesser spirit: gods and archangels don't generally do this. Neither do lwa or orisha: they may ride a horse but they depart when the ride is finished.
Those who can see spirits will frequently see something hovering around or just within the auras of those suffering from spirit infestation. Those who can't will sometimes note that the person "doesn't feel right" -- their eyes are "weird" and their aura feels "tainted," like you're standing next to a sculpture made out of rotting meat. Unfortunately, this is difficult to replicate in a laboratory and so it is hard to use these guidelines as hard and fast rules for determining when infestation is taking place.
It also appears that in cases of infestation "like attracts like." Someone with anger management issues is likely to get infected by a wrathful spirit, greedy people may host spirits of avarice, sexual obsessives become prey to lust-spirits, etc. Since the Goetia focuses primarily on working changes in the material world, it's not surprising that those who use it are generally greatly desiring a new sex partner, more money, an ass-whipping for a hated enemy, etc. And since the Goetic spirits appear to be closer to and more interested in this material plane, it's not surprising that they both work more quickly and are more likely to stick around and have some fun with their new host.
Again, this is all rather preliminary. I think the nature of spiritual oppression needs more careful analysis and discussion. The term gets bandied about a lot, and most working magicians I know would agree that such a thing exists. But there's no clear-cut definition and little in the way of theories as to why it occurs, what the spirits gain from oppressing individuals, and how spiritual oppression relates to other forms of spiritual or etheric alteration or damage.