The reason they are locked in the Circle of Magi is the fear that they become abominations, or, possibly, even the fear they may try to pull a Tevinter Imperium, enslaving those without magical abilities. They are locked up and persecuted by those who don't have magical abilities, and, who fear the unknown that is magic (unknown to them, anyway). Locking up people for life for events that might happen is just plain wrong.
Commendable in abstract, often iffy and less than uniform in implementation and in the details.
Would you apply that towards life imprisonment for a serial killer, or capital punishment? There's no way to reverse the killings he's done in the past, so punishment doesn't rectify the harm, but any future killings are just hypotheticals that might happen until they do.
The common accepted answer to that is that it would be an appropriate function of justice- that the fact that the person has already harmed people warrants the punishment.
But what about someone who hasn't yet done so, but had the ability and intent? A would-be perpetrator who attempted a catastrophic act of terrorism? The idea of retributive punishment wouldn't even apply there, because there was no harm. Even though they had intent and capability, what is the moral and ethical basis for detainment for long periods of time, or effectively their life?
The obvious answer would be intent. But intent isn't always necessary to harm one's self and others. Sometimes simply capability is enough, when it can't be controlled and real harm is possible, yet not guaranteed. Which certainly applies to mages and magic, thanks to the involvement of spirits.
So the better question would be- would you apply that same viewpoint to the idea of a quarantine?
Right now there are people in Uganda who are literally being locked up for the rest of their unfortunately very short lives if they are found to have Ebola. There's fear, there is misunderstanding, and there are even resistance and subversion groups, friends and family who try to hide their loved ones and escape the quarantine. Is this wrong? Is this bad? The carriers of Ebola aren't malevolent. They aren't deliberate spreaders. They are, in every respect, the first victims. And most of them are now going to be locked up for the rest of their life on the basis of what might happen if they aren't.
The current outbreak of Ebola is a death toll well within the scope of an abomination outbreak in Dragon Age: slower, but they can be modeled in similar ways. Of course, there are limitations to this analogy as well. Ebola, as devastating as it is, either burns itself out or is survived. The few survivors are no longer potential carriers by the time they are allowed out of quarantine. Mages never stop being potential abominations- or, to apply the analogy, mages never stop carrying a latent stream of ebola that could come out in a period of emotional weakness.
Does that mean they shouldn't be quarantined, shouldn't be locked up for the rest of their life just on account of what might happen?
To some people, certainly. I imagine that the world would also survive an uncontrolled Ebola outbreak- though certainly not in any form that people who value that status quo would appreciate.
I'm not saying everyone gaining magical abilities would make everything equal or not be somewhat chaotic, I probably worded it...weird or wrong, but, that if everyone gained magical abilities, that, the discrimination that went on before the event wouldn't be as bad, and, it would possibly allow EVERYONE to look at magic in a new light, and let Thedas reorganize the system of how it trains magic users in the proper use of their abilities into a more fair, less abusive, and less racist and fear-mongering, less 'what if?' system.
That only applies if fear and chaos is just a result of misunderstanding and ignorance. Sometimes fear can be just as strongly rooted in the knowledge of what can be done and how. Guns and nuclear weapons are scary to quite a few people, even without superstition. Giving them to everyone doesn't make it any less frighting, especially if you are intelligent and well informed about what they can do and just how precarious they can be.