First of all not according to me but according to us as humans. I'm sure wherever you are from your nation has tolerated its horrendous acts in the past because it was for the greater good of the nation. Everything can be branded as "its for the greater good" but we must see how true that is.
Ah, but the very notion of "good" is subjective. Therefore, since you were the one that first used the term, I must go foward with your own notion of "Greater Good" in mind.
All authority figures are mages indeed, but we know for a fact that it takes a lot of effort to get there. Who your father is is completely irrelevant in opposed to southern Thedas nobility system. You need to prove yourself aka excellence is awarded.
And how do we know that for a fact?
We do know that the highest class within Tevinter is entirely decided by blood. Where exactly is the evidence that family connections are not more important that pure magic ability? Do we have an example of someone being born and becoming an Archon or even just a Cleric?
I don't think we do.
Besides, the Tevinter system is a nobilty system through ahd through since it relies on an inborn ability to decide who rules.
At least, in Southern Thedas, anyone can become a noble; it's rare but, theoretically, it can happen. But a normal can never become a mage.
Fenris was free and living in a bloody mansion in southern Thedas. In comparison to what we see in slums that city elves live in most slaves have a better life in Tevinter when compared to city elves. being treated like property is better than being treated like trash.
A bold claim considering that we've never seen a slave in Tevinter.
We do have evidence of one run away slave living in a slum in Ferelden and prefering it. And we do have examples of attrocities commited against slaves.
there is no guarantee the said mage will be dangerous.
All mages are dangerous through and through.
Southern Thedas owes a lot to mages and they know it as well, but they have forgotten.
If they had, they'd just kill the lot of them.
The Circle exists precisely because mages are dangerous but useful.
All I'm saying is there are ways to make the life of mages better at the circles but there is no such opportunity for slaves as long as they stay slaves.
Foregoing the fact there are different types of slavery, we could find ways to sustain Tevinter without slavery.
But if you want to claim otherwise, I can also claim the pre-rebellion system is the only way to prevent the subjugation of non-magical society.
And I can come up with arguments, ask anyone.