Coming from my first impressions of the anime Shinsekai Yori, this series is fairly hard to follow, at least for me. So I just wanted to write down the points I've grasped and maybe get some feedback from others that have watched the anime or even the manga, novel, whatever flavor you rock with.
To start the characters in Shinsekai Yori aren't that interesting, which is weird for me because I do like good characters and yet I'm still watching this anime. The real draw is the setting and all that heavy lore of this small village.
The behaviors of the villager and the surface level understanding of cantus that most of people have, is what made me come to this conclusion. The village itself I would consider a cult, which seems quite obvious in the way the anime chose to presented information to both the characters and the viewer.
Brainwashing
Early into the series we get exposed to the "Cantus Ceremony", which all kids have to go though to activate their cantus. The main focus of the brainwashing was to prevent them from harm other people with there cantus. Quiet a noble cause if you only look at it from a distance, but looking closer in, we see this weakness is easily used to control and have an advantage over the people effected by the ceremony.
An example being when Mamoru, Maria, Saki, Satoru, and Shun went in the forest, where they were being attacked by several qeerats. A priest finds them and because of the information they discover, all of their cantus were sealed away fairly easily leaving them powerless against the swarm of qeerats on their tails.
Hidden Secrets
With the appearance of demonic slugs and Saki's quick thinking to intimidate it, we find out the slugs doubles as library for cantus and village history not told to regular villagers. Diving us head first into the sea of information and lore for both viewer and the characters present.
The gist being cantus was being used as a weapon, and several other grim acts, earlier on in this cantus history. In order to stop the corrupt users of cantus from doing other unpleasant acts, they forced on this program for all children showing signs of any physic powers. Essentially this was the start to the brainwashing and the end result is the isolated village they live in now.
Suppress Opposition
Becoming self educated of what is going on inside the village, the leaders would want to halt any kind of leaked information and prevent any kind of opposition from rising up. More or less we have this in the case of the more recent events of Shun becoming a karma demon.
At this stage they can't do much in preventing him from completing the transformation. We also learn a bit more about cantus with its problem of subconsciousness leaking out and making it harder to control it; at least thats what is happening to Shun with the transitioning from human to karma demon.
Clarification
That is the sum of what I have deduced into a somewhat compact form, some details might not be as accurated, but I think most of the general knowledge is correct. If anyone can give me more information I might have missed, without spoiling future events, that would be helpful in clarifying this series for me.