"Just say no" doesn't work. There are a number of real life examples I could name except for the fact that some of them a RL touchy subjects. Rote resuscitation doesn't work. Thinking critically works, developing will and sense of self works. Learning how to use magic in Thedas isn't just how to light a fireball. Circle mages are actually educated in what the Fade is. Saarebas not so much.
Ideological indoctrination does work- and that's part of the horror of it. Psychological conditioning is not simply rote memorization, it can actually change how your mind works and understands things- and in so much as it doesn't work, neither does relying on critical thinking alone.
Does it work on everyone? Of course not- but in the case of the Qunari, the people who it doesn't work on, and who don't get on with the party, are liquidated. Saarabas are the survivors.
And yes, it's resisting Pride, but part of the point was recognizing the danger. A Saarebas, who has no understanding of the Fade, no understanding of the rules has a better chance of being possessed or broken because they don't have the knowledge.
https://www.youtube....XCpKDqFb8#t=706
Interview with Gaider. Which, ironically, points out that their training is make fireball this big and that's it. It's a weapon, and weapons don't think.
Your Gaider interview works against you- not only does Gaider NOT say that formally untrained mages have a higher chance of being possessed, but he equivicates the Sarebas magical style to hedge mages- which we know exist, and continue to exist, even without formal magical knowledge and training. Gaider doesn't- at least not where you quoted him- say that Saarabas are exceptionally prone to abomination.
Meanwhile, the fireball analogy I brought up was as applied to Circle mages... and, since we seem to agree that bigger fireballs =/= better resistance to mages, emphasizes the relevance of mental fortitude rather than magical firepower. And since the Qunari do know enough about the Fade to know how dangerous and deceitful demons can be...
Saarabas aren't innocent children who don't understand deception or demonic threats.
Put it in a situation where it can be fooled into "taking orders", and boom. Circle mages can be fooled, but it's not because they can't think.
Saarabas can think- and understand the Qun. It's not merely 'taking orders' from whatever voice appears, or else the Saarabas system we see (in which, hey, Saarabas have a lot fewer abominations than all the critical-thinking mages we see) wouldn't work.
This isn't even touching on the nature of the Fade- and the limitations of spirits to understand mortals, let alone abstract concepts as complicated as the Qun. Even Sten, who is by no means a magical expert or experienced, is unfooled by the fade illusions.
Another funny bit: Arvaarad means one who holds back evil. You keep telling someone they're evil. They're going to start believing it. Rote education does not help.
Ideological indoctrination, however, does.
The Saarabas do not believe themselves evil. They believe themselves dangerous things- but can still find a place, and enlightenment, and a sort of salvation in the Qun.
Saarabas who do not believe these things, of course, get weeded out with the rest of the ideologically unfit.