"Cult" I just love that word as it does so fit so many "Christian" organizations. I do not think the people who did this were demented at all just in strong believe with the "Religion or Deity" that what they were doing was the correct thing to heal the person.
That or those being injured er helped were in position to cause some mischief in the inner sanction of their "religion".
Do not mistake ignorance couple with strong desire to belief in what a person is doing is any less then just that nor any more. Ah what great devastation could be brought to the modern time from solely practicing the old testament in the Bible with no real knowledge.
Let the blood rivers flow from thine alters and I hope you are not a leper.
I don't know if it is Human Nature, but it seems that Obsession with an ideal is a massive part of our Psych as a species. Religion is fine if it is a personal relationship with what is perceived to be Divine. What takes it to a frightening level is the Power and Control over people administered by the few over the many. When this immense power is used to direct the flock to reach aims of Politics, Race Hate, Capital gain or simply earthy pleasure, perverse or not, you have a very dangerous situation. Many societies are Religious but they are far from Spiritual.
I know this is going to sound like a stupid question, but did they like remove the devil?
What we have is a fear of what we don't understand. A "Devil" can be simply a state of mind that is not "normal" for our culture. So attempts to drive it out are prescribed by those who fear they will lose their power.
Many truly gifted people have been persecuted and hurt because they are different or appear to pose a perceived threat to those who dominate society.
Witch hunts go on today as throughout the ages.
I think you are right the fear of losing power is among the top motivators in our race. So rather then admit they do not understand what is wrong with a person remove their eyes and claim it was a demon. In the old days this worked very well as the person most likely would have ended with blood poisoning (gangrene) cause delirium and masking the truth even deeper.
This reminds me of the recent cases which made the news of person tracking down, and hacking to pieces albinos (I think it was an albino family) because it was viewed that the body parts could bring people good luck. This highlights the extent people would go to to carry out what they believe in and how easily they can be blinded to if their actions are hurting anyone or not. As far as they see, they are trying to do the victim good, like save her soul. They get so caught up in what good they think they are doing that they can't see how it would look "from the outside".
It's easy to blame the devil when he isn't around. I'd put it down to cross wires somewhere in their skull.