Connor is psychologically damaged. "It was all me" is simply not true. Connor's story may serve as a cautionary tale, but where he went wrong is when he let the demon in, after it manipulated him to do so through his desire to help his father. That's what people should focus on when they use his story as a cautionary tale. Whatever the demon did later wasn't Connor.
Well...yeah.
A normal kid would have mourned. A mage kid destroyed one of Ferelden's major towns.
With regard to the Circles, his story actually showcases the problems with the Circle system: if the Circles were schools instead of prisons, the parents of mageborn children would be rather less likely to hide them away. If being mageborn wasn't regarded as a social stigma by the nobility (because mageborn children can't inherit), the girl from Chateau d'Onterre might have survived to become a capable mage.
There is some truth in that. Fear of the Circle does lead to a certain number of incidents.
However, if the restriction of the Circles are lessened, we risk thier efectiveness. And there are always going to be a few families to whom the prospect of any restrictions are too much.
Connor was a noble. There is no way Isolde wouldn't have been able to visit him.
The scenario with Vivienne as Divine is probably the most stable one with regard to the situation of the mageborn, and it is admittedly a marked improvement, but it won't change that for many mageborn, their sojourn in the Circles will feel like life imprisonment, for no fault of their own. This is especially true for those who don't buy into its ideological premise, don't follow the party line. I think it is worth some risk to try and explore alternatives.
Why?
And that is a serious question.
The Circles provide luxurious accomodations, food, safety, education, etc. They actually allow mages to have an higher standard of living than most people in Thedas.
Certainly, there can be abusive Templars but certainly no more than there can be abusive nobles or guardsmen.
And they may be stifling but just how much social mobility does the majority of Thedas has in reality?
So, that is what they risk if they remain in the Circles.
But, if mages are free, normal people risk literally everything. Their livelihood, their homes, their families, their freedoms, their lives.
Why should we risk everything for a hundred people so that one person feels less restricted? I honestly can't see any justification for this.
Which is not to say that there can't be alternatives. I have just never seen one proposed that couldn't be defeated simply with "greater exposure to a greater number of people with increased Templar reaction time duet to distance from the mages leads to a greater number of deaths when accidents happen" or "Power begets power. If their magic is not restricted in some way, they will rule society in a couple of generations."
It tends to be just "train them and then release them on an unsuspecting population."