Vivienne explains that all mages can live outside the Circle- with the permission of the First Enchanter. All Circles are different, but she says that Kirkwall was an extreme case that was not representative.
But can we trust what she says? Bioware games don't usually actively deceive you through the NPCs but they do often promote perspectives that aren't representative of the entire truth. Vivienne's account conflicts with numerous others heard over the course of three games: which to we consider more valid?
Vivienne is clearly enormously invested in maintaining her power base and social status. She is also a consummate politician and player of the Game. I don't doubt what she says has some truth. We know that Kirkwall's Circle was one of the most repressive. But this doesn't change the fact that her experience, based on everything else we've ever seen of the world and its treatment of mages, is extreme in the opposite direction. That her Circle apparently hob-nobbed with the nobility and encouraged its members to take positions as exotic members of the court doesn't mean that's normal.
In DA:O it's stated at the Circle in Lake Calenhad that it's extremely rare for the First Enchanter to give permission to a mage to live or even travel outside the tower. Wynne wasn't allowed to raise her own child. Freedom of communication with one's family - freedom to have a family - were both severely curtailed at a Circle that has not been waved about as "the one bad apple that spoils the bunch". And it certainly didn't seem like living outside the Circle with the First Enchanter's permission was as trivial to achieve as Vivienne makes it sound.
Even if Kirkwall's circumstances were extreme, Divine Justinia ordered an investigation into it and did nothing. Whatever the reasons for that decision, and however complicated they may have been, it makes it hard to argue that there's nothing wrong with the current system when rampant abuses can be investigated by the highest moral authority and excuses found to leave them as it is. There but for the grace of Andraste go I, and all that...
I actually don't hate Vivienne at all. I don't personally like or agree with her, but I find her fascinating, and from what I can tell, if she is made Divine even she would institute changes designed to curtail abuses of Templar power and to provide Mages within the Circles with more self-governance.
But her off-hand dismissal of most of the rest of the lore regarding the freedoms actually available to Mages is deeply suspect and I don't think we can use that one line to promote an unexamined assumption that Mages can all go live wherever they want with a permission slip.