This is a theory on both our parts. Neither of us has any concrete, undeniable evidence to support our theory, it's just that.
That abomination and mage costs acceptable in Tevinter are socially unacceptable in White Thedas? Er, we do have concrete, undeniable evidence: the Circle System,Tevinter's deviation from it. Both are the reactions of the effective power centers of their respective societies to situations that were deemed insufficient.
I see more evidence to suggest the casualties are relatively low than not. Tevinter already spends a lot of money on lyrium and slaves for blood magic. Their resources are finite, just like their populace. I'm not convinced the arguments that the losses are high and just soaked are more substantial than the argument that they must just be better controlled. I acknowledge that both of these theories are just our opinion based on the evidence we can scrape together. It's possible that your theory is right, but I think there's also a strong argument that it's not.
I'm honestly confused where you think financial or population sustainability costs factored in at all. That's not the argument being made by most people who raise the spectre of abomination casualties: the argument is 'dozens or hundreds of casualties in an outbreak is too many to tolerate', not 'dozens or hundreds of casualties in an outbreak is too many to sustain a population.' Toleration is a matter of a willingness to accept costs: population sustainment is a matter of a mathematical ability to accept costs.
Given that Tevinter regularly and systematically absorbs and ignores mundane costs in other fields (like, say, mageocracy, slavery, and a voluntary war), I have no idea what standard of proof you would require to consider the idea that they might not care much about mundane casualties from an abomination outbreak so long as it doesn't threaten their power. Which in and of itself is a huge range short between 'too many casualties to sustain' and 'superior results.'
My opinion is that the casualties have to be pretty high to constitute the lack of freedom of a decent sized portion of the population. It's not an objective argument, but it's not any less objective than any other.
What constitutes a decent sized portion of the population? Mages aren't one in ten, or even one in a hundred. They may not even be one in a thousand.
I wouldn't think the concept of freedom would be terribly alien to the people of Thedas, though. After all, Andraste was an escaped slave. Their whole religion is born out of a respect for freedom.
Freedom from what? What was Andraste rebelling against, and who were her enslavers?
The Andrastian religion was born out of opposition to mage abuses, not a western understanding of universal human rights and political freedom. Freedom means many things- in the Andrastian context, 'freedom' was in the context of safety from mages, not empowering them to repeat it.