1. The thing is that even the original demon ("one of the rarest and most powerful," in your own words) is dangerous, and it becomes more so by possessing Connor. A "middling competent mage" probably would have been trounced by an abomination of desire, if not forcibly co-opted the way Teagan and presumably the guards he fights you alongside were, and then the town is arguably worse off than it was with Jowan in the cell because at least Jowan is still alive and willing to help. True, a middling competent mage might have taught Connor well enough to avoid this peril, but since we hear a shade of presumably-actual-Connor shouting "I'll help him! You can't stop me!" in a child-who-thinks-he-knows-best-and-won't-hear-naysayers tone, that's a questionable assertion. The one thing we can be reasonably sure would have stopped this is if Isolde had bitten the bullet and handed over her kid.
2. The Circle's intended purpose is to teach mages discipline, the way Jowan was supposed to be doing with Connor. A handy side benefit is that the mages (who really could be compared to bombs, though obviously that's not meant to be one-to-one; there is in fact nothing in the real world we could one-to-one compare to a mage) are surrounded by other mages and by templars, with a small number of priests around who represent probably the only civilian casualties of the events of Broken Circle. You're right that fewer civilians are caught in an Annulment than are caught in an abomination attack outside the Circle, but I don't think you're really giving that point the attention it deserves.
3. Apparently DA2 establishes that people who are cured of possession the way Connor was are diminished mentally by the experience, and Connor certainly seems more vulnerable to despair demons in Inquisition than he seems to have been in Origins. And despite this, he wasn't Tranquilized. To say he would have been before is fairly questionable.
4. Again: my argument isn't that most hedge mages don't turn out fine. My argument is that stuff like Connor gets up to is not impossible if they don't.
5. Also debatable. The Rage Demon a Mage Warden fights in the Harrowing implies that he intends to forcibly possess you, and the story of the Staff of Violation concerns a mage who almost certainly wouldn't have consented to getting possessed.
6. Mages are apparently easier for demons to find, partially because their minds react differently to the Fade than a mundane's does. And even if I'm wrong there (I don't think I am) the fact is that a mage is a better host for a demon because possessing a mage means the demon is more magically powerful than they already were (even if it's not by much if the mage is Connor.)
7. I do. She has responsibilities to people other than her son. An entire village of them. And as a noble, especially a regional-top-dog noble, she should know that better than anyone.
1. Teagan was entranced, not forcibly coopted, exactly like the templar in the Circle tower. The desire demon offered him something illusory he desired under a mild hypnotic effect (meaning he retains free will), and he took it. He'd fallen a bit further down the rabbit hole when we met him; it'd been a while. The same would be true of the guards. It slowly deceived one after the other over time, not all at once. We just come into the picture at the last possible moment.
You're right about Connor's willful agreement to possession. He was tricked into thinking the demon would heal his father. That was his desire. If he had been taught better, he might've recognized what was really going on. If Jowan hadn't brought that on Eamon in the first place, he wouldn't have been vulnerable to that desire at all.
2. Discipline's only part of it, part of the character a mage needs. Another part, the guile, means you've learned to recognize tactics used to lure you in, so that you don't fall into beguilment, the same way Teagan, the soldiers, those templars, or our party in the fade did. Willpower, which is perseverance in this case and the will to say no to whatever they're offering, that's another part. Discipline like we tend to associate here applies more to the regimented thinking a templar would usually be prone to. Maybe that's part of their problem. I love the way Morrigan talks to spirits, if you've used her to free Connor or taken her in the fade section of Broken Circle. She's not having it. lol
I don't think you can compare a mage to a bomb more than any other person with access to weapons (or a high enough intellect, martial training, etc.) They are able to do a lot of damage, but they have the power to say no. They can choose if they are going to fall into that or not. Convincing themselves that they can control the demon as an abomination, that's just as much a delusion they have to be mindful of. Yes, a lot of people can die when one gets out, just like a lot of people can die when a regular joe flips out, but it's a question of values. Freedom vs. Security. I'm on the side of freedom. If your security oppresses my freedom, then you've overstepped your bounds as far as I'm concerned. So that applies to the whole circle system to me, especially considering all the examples of plenty stable mages we've got, the great majority. Usually when we have seen them slip, it's because they're under severe duress, often from templars.
3. There's more than one way we can cure Connor though. With high enough willpower, you can just order the desire demon to release him outright (while in the fade). Blood magic vs. no blood magic, etc. He seemed fine to me in Inquisition. Guy has a lot of guilt on his plate, but he was well adjusted.
I don't think it's questionable to assume. Mages are made tranquil because of their lack of willpower. In other words, they're too gullible or prone to temptation, in the view of the templars overseeing their harrowing. When confronted with demons in the fade, are they resistant enough to the influence of fade spirits? Connor obviously failed that test the first time.
4. Not impossible but not likely. Every time I get in a car, I could crash, but it's not likely if I know what I'm doing. It could happen, but I'm betting it won't. And if something does happen, I'm betting I can manage it well enough to get through it. Same thing. I don't need instructors in the car and a police escort every time I might drive to the store. Which is where I'm saying Isolde tried to do the best she could for her son. Unforseen circumstances derailed the plan.
5. I read the story on the staff of violation, but I didn't really think about it relating to this at all. I've forgotten it, now, so I can't say. The rage demon in the harrowing, again it's a question of willpower, perseverance under stress. It can't just knock you out and possess you. You're not physically in the fade, so it's a test of minds, an abstraction.
6. No, you're completely right here. I just don't agree they should be cloistered off because of it, under guard at all times, removed from their homes, etc. Freedom is worth the lesser security.
7. Being a noble is what gives her resources to train her son privately and keep him out of the Circle. It's in a codex somewhere that nobles sometimes attempt to do exactly what she did, so I imagine that's where she got the idea. Loghain obviously had Jowan on retainer. I'm sure he's not the only one in her social circle. Yes, she had a village depending on her family, but she took reasonable steps. She was just betrayed by a snake false friend.
edit: By the same token, our player characters travel with multiple apostates and hedge mages. By that standard, all of them should've been in the Circle. Granted bad things can happen with all of them except Morrigan and Dorian (Tevinter non-circle mage). C'est la vie (sp

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