I see... so in Rivain, where the Seers openly welcome spirit contact they're not trying to be possessed because they don't have the Chantry fear.
And Solas doesn't say he always guards against demon possession... because why would he? He doesn't have to fear spirit possession because he doesn't have Chantry fear.
And the Avvar never get possesed... and the Chasind and Dalish never get possessed... because their perceptions are totally different from the Chantry.
Only... they all can get possessed.
And before you argue - yes, but the Fade mirrors thought - there are far more people who don't subscribe to Chantry fear than do. Nevarra doesn't. Tevinter doesn't. The Dalish don't. Most mages don't. The Wardens probably never think about it. Rivain of course.
I believe you are grasping at straws solely because you hate the Chantry... and you hate mages being hunted like cattle by demons and want to place the blame squarely on something else.
It was an interesting facet of the cosmology of Thedas... and now, it's mostly gone. I don't care "why" - it's just my opinion that the direction the cosmology is taking is boring me.
You are pulling a false dichotomy here, I never said that mages from other societies can't get possessed, I said that the rate at which that happens is evidently lower than in Chantry circles which supports the view that locking mages in a tower like prisioners and driving them into depression, vengeance or paranoia provides no actual benefit in protecting the world from abominations.
Rivaini seers offer themselves as willing hosts for positive spirits who enter and live as they want, they actually provide benefitial services for the communities they live in. It tells a lot about Chantry understanding of magic when they called the Right of Annulment against the Rivaini Circle because they followed a practice that helped their society for thousands of years.
You are the one grasping at straws and trying to discretid the plight of all mages because the stupidity of a few, in Godwin's terms it's the same as saying that because a few Jews are corrupt bankers who try to control the fate of nations then all Jews must be confined with the threat of death to prevent the rest from being like that.
This is essentially what the devs said on the subject.
The Dalish can, if you do things wrong, lose one clan per game. Two of those three clans are in that position because that clan's mages were irresponsible with their magic. And if the PC's intervention is the reason Zathrian and Marethari's clans die (in world-states where they do,) it's not like it would have been impossible for the powder-keg they lit to destroy those clans in any other way. And then there's the fact that at least one clan abandons spare mage children, and what happened with Imshael. Not to mention that Merril explicitly states that they've lost clans because the Keeper went abomination. In short, the Dalish are better evidence against mage freedom than for it in a lot of ways.
The Avaar, meanwhile, conduct rather risky religious rituals in which they invite spirits into their territory and their mages bodies. They've managed not to screw that up, if you don't count Hakkon, but that's not the same as saying you can promise that will stay stable.
We don't see much of Rivain, so we don't know that this is true, but according to Word of Gaider there's a higher rate of abominations there than in the rest of Thedas. They accept that they can't really stop the problem, which means that it's not as mitigated as in the rest of Thedas.
In short, I don't know that I'd say "these societies have remained stable."
And I didn't think we knew enough about the Chasind to make any argument about them whatsoever.
Zathrian had his children killed and raped, you want any father to remain sane after that? He cast a curse on the perpetrators which ran out of control after they died and the caster refused to let go off his hatred of humans.
Zathrian's curse made him immune to age and kept spreading until the spirit he summoned with blood magic decided she had enough and started attacking elfs besides humans.
Still, a centuries old mad Keeper does not represent the Dalish mages by a whole. His apprentice Lanaya followed the best of what he taugh, turned her back on hatred of humans and in turn used her magic to make her people prosper for a long time.
Marthari's clan can also be counted as an exception, Merril deliberatedly went against the wisdom and guidance from her teacher and started using blood magic because she placed the restoration of an ancient artifact above the safety of her own clan.
A single Dalish mage from a single Dalish clan choose exile over stop dabbling with the most dangerous forms of magic possible which resulted in her keeper giving up her life in her place, that was the sole casualty directly provoked because of Dalish magic leniency. The clan getting wipped out wasn't because of a demonic possession but because they attacked the freaking Champion of Kirkwall in grief over the perceived murder of their leader at the hands of Merril.
Compare those examples with circle mages who were supposed to be less vulnerable to possession and whose possession would be better fought by templars.
Uldred, a Senior Enchanter, became a Pride Abomination, corrupted a large number of mages into a blood magic cult and completely ravaged Kinloch Hold despite all suposed safeguards that the circle system should provide over free mages.
Orsino, the First Enchanter of Kirkwall, was a blood mage under the watch of the most psychotic and paranoid Knight Commander ever and the game explicitly states that he and most other blood mages in Kirkwall turned out that way because the circle system and templar oppression and corruption drove them off the deep end.
Last of all, the Dalish don't abandon magic children because they prejudice magic or because that increases the risk of abominations, they abandon magic children because too many mages in one clan would attract the attention of templars wanting to attack the non-andrastian apostates.
Oh rly, almost every dalish clan we saw had problems caused by their mages and said problems were involving demons and Avaars caused threat on world scale by playing with demon twice and we learn that five minutes we start exploring their culture wonder how much more dirt one would find on them with more exploration. On other two, we never had opportunity to explore their cultures or even region, so i don't know from where you took your statistics but in fact we know that mages going wrong happen in Rivain. Then there is matter those group have to deal with significantly less mages than circles.
Good intentions or bad mage mage still remains threat.
Again, how many times did Avaar mages nearly caused a catastrophe? Twice in a thousand years!
Let's hate and persecute generations of mages from hundreds of different tribes because two mages from the same one did some bad ****. GENIUS!
The problem are not Avaar mages, the problem are the Jaws of Hakkon and it was a ****** MAGE who saved the world by stopping them the first time.
The Chantry ripped the real Ameridan from the records alongside Shartan because a massive war broke out between elfs and humans so every heroic elf and mage was retconned into non-existence or being a devouted andrastian human muggle.
Magic is dangerous but is also a part of nature like fire, storms and winter and you just can't really suppress it. In some instances it put the world in danger but so did normal means like wars between nobles and kingdoms.
There was nothing magical about the Exalted March on the Dales which was started by and mostly fought by swords, shields and arrows, there was nothing magical about the Qunari military superiority that nearly conquered all of Thedas until setting the mages loose turned the tables and there was certainly nothing magical about Gaspard nearly driving Orlais into the ground over his rivalry with Celene.
Half the problems in Origins were because Loghain was paranoid about an Orlesian invasion in the middle of a Blight and that was because he previously fought an Orlesian occupation which had nothing to do with magic.
Even Tevinter, despite being the greatest example after Arlathan of magic gone wrong, still stands as the oldest and strongest civilization in Thedas because they valued magic instead of fearing it.
My point is that oppressing and persecuting mages because magic is dangerous and some mages can royally screw up never helped reduce the problem, creating the circles and placing the templars to treat mages like crap ultimately made the problem worse because it turned mages against society at large and provoked a continent shattering war.
In a nutshell, if measure A didn't help reduce problem X then imposing measure A to confront problem X while creating problems Y and Z was not just pointless but a shot in the foot.