That's because everything is their [the rebel mages] fault.
Mage blows up a Chantry and a Grand Cleric, not long after that another mage tries to assasssinate the Divine. Their reaction? "Hey I know! Lets start a rebellion, attack the [much more popular] templars and cast down the circles [the one thing 99% of the population thinks keeps them safe]! That'll prove we're on the up and up!" herpaderp
I won't go into the events that kicked off that rebellion. Varric already summed it up quite nicely at the beginning of the third act of DA2. Suffice to say that the mages didn't just rebel for no reason.
Turns out that Vivienne is right about them not being able to win. Storyline-wise, they need to pledge themselves to Tevinter to avoid being crushed. Gameplay-wise, the rebel mages in the Hinterlands have hired sellswords to tank for them because they'd die too easily without them.
So maybe Fiona made a big mistake, but I think something needed to be done. If Kirkwall were truly the exception and most mages were treated fine, the original Cole would never have died, and the members of the Starkhaven Circle would have had no reason to run in DA2. As best I can recall, Vivienne doesn't suggest any alternative besides "Do nothing. Just be good little mages and hope you're not one of the ones they arbitrarily make Tranquil." I could be forgetting something. If so, tell me.
And that justifies killing every Mage in kirkwall and subsequently getting rid of all those oriviledges Vivienne loves to talk about for something they didn't even do?
Would you still say the same if Meredith decided to kill all Fereldens in Kirkwall because anders is from Fereldens?
Anybody who thinks that Meredith's decision made a lick of sense--either in-universe or out--has something wrong with them. I really can't stand Sebastian most of the time, but he's the only one who bothers to suggest punishing Anders instead of the Circle after the Chantry is gone.
Of course I can. We do not see such fear with the Dalish, Chasind or Rivvain...where you have mages living cheek and jowl with non-mages for centuries or more. The people in the White Chantry nations fear magic because they are generally uneducated and ignorant towards the way it works. And keeping the mages and the rest of Thedas separated merely widens the gap between them, resulting in neither group understanding the other. And that's the fault of the chantry and the templars. But with enough education people might start to understand magic better, and thus naturally become more tolerant of mages. And if more was done to integrate mages into society on a normal level and the stigma were to disappear, I think far fewer mages would succumb to demonic suggestion as well.
E.g., Sera. The girl actively tries to be ignorant. I took her and Solas to the tomb where Solas talked about about the old Emerald Knights. It wasn't a long and boring lecture or anything. He just says something like "Some people say the Emerald Knights were great heroes, and others say they were bloodthirsty murderers. Both may be true," and Sera responds by blowing a raspberry.
Like "Shut up Solas, stop making me learn things! I don't want to learn anything, not even for ten or fifteen seconds!"
I figure that's why she's so scared of magic. The people who raised her told her all kinds of horror stories, and she doesn't want to learn any more about it. All she knows is "Magic=Bad" and that's all she wants to know.
But anyway, back to Vivienne. Her statement about how people fear mages because of children accidentally killing or injuring people is stupid.
You know how you teach people not to fear mages after that? Even stupid people like Sera? You tell them "It was an accident. This building burned down, but even a child without any magic could have burned it down by playing with fire irresponsibly. The answer for a non-magical child is to teach them what not to do and how to safely build a fire. We are going to take this kid away and teach her what not to do and how to safely use the magic. Then there will be no more accidents, and she can even use her power to heal injuries and save lives."
If ignorant peasants were told this kind of thing all the time, then I believe it would at least reduce the number who saw all mages as boogeymen.
Tevinter does not have or does not appear to have lots of abomination cases because magic is prevalent there. Many people practice it. Magical education in Tevinter is also top notch. That could have something to do with why there are no mentions of abominations. I'm guessing if you cannot resist a demon in Tevinter you are seen as a weak wimpy mage.
That's my impression as well: who keeps abominations from running amok in Tevinter? Other mages. It seems to work. And Dorian was very open about what was wrong with the Imperium, so he surely would have mentioned that if it were a problem.
On the subject of Tevinter: from all that the NPCs in the different games have told me, very few of the Imperium's problems are because of magic. They have slavery and those slaves are abused and sometimes killed, but that's because people made a bad law, not because of magic. As for the Imperium being ruled by mages, well, how is a ruling class of mages any worse or better than a ruling class of people with noble blood like in Ferelden and Orlais? Soporati may have to resign themselves to having no say in affairs of state in Tevinter, but non-nobles have to resign themselves to having no say in affairs of state in Ferelden.
Ideally, in any nation, those who make the big decisions would be those most qualified to do a good job and do the right thing. That isn't the case in any of the nations I named in the above paragraph, and it would be very good if they all reformed. But I'm having a hard time seeing what makes Tevinter drastically worse than Orlais or Ferelden. Blood magic, using unwilling victims, to gain or cling to power? No, I don't suppose they do that in Orlais, but they do abuse their subjects in non-magical ways.