"Displacement" was a euphemism; a lot of people were being killed. And slavery is also perfectly legal in Antiva, in addition to Orlais' totally-not-slavery-we-pinky-swear, not to mention the Qun's mageless thought control and various forms of standard class-based oppression.
Also, that's not true about "every single blood mage." Jowan was a well-meaning doofus, and the injured blood mage you encounter in Broken Circle came across as quite sympathetic. And in DA2, Alain was also a blood mage and remained highly sympathetic; Gascard DuPuis, too, was at least redeemable.
A lot of people were killed? Where does it say that? The war table mission talks of scuffles between the supporters of both nobles, but it was not an all-out war or anything like that. I'm sure there were deaths, but a lot is stretching it.
Yet we never learn of mass mistreatment of slaves there (apart from the Qun qhich stands on its own in terms of oppression). You are right that I overlooked Antiva, but it seems nowhere near as bad with slavery as the Vints, who go all the way to Ferelden to fetch slaves and don't even hesitate to kill a roomfull of them if it saves their skin.
Jowan was not an *******, granted, but he was an irresponsible dummy who caused way too much trouble. The mage in Broken Circle stands unapologic after helping cause the mess the Circle is in. Alain was forced to be a blood mage as Kaiser said. DuPuis was admiring a serial killer's work and wanted to learn from him, that kinda fits the definition of complete ******* don't you think?
Next to that, we got the aggressive blood mages in Broken Circle, the Tevinter slavers in the Alienage (including their mass murdering leader), the guys you kill in a sidequest in Denerim, Grace and her followers, Idunna, Denerius and his underlings, Quentyn, Orsino, the blood mage you fight in The Final Straw with all the demons, the crazy elf guy that comes back for his ex girlfriend, the one who willingly turns into an abomination to fight you in Act 3, that crazy girl in Act 1 with the dopey makeup, and several others in DA2 I can't be bothered to remember because that game had so many blood mages.
The games definitely do not support the notion that magic, especially blood magic, does not corrupt the user. Dorian in particular says that it drives you to always seek more, so while you could have good intentions at the beginning it's hard not to end up killing people to light your candles. And as someone who has lived in Tevinter, he has seen more blood magic than most.
Oh, one aversion I forgot is Avernus. Who is kind of an ass and helped precipitate the Warden's fall, but they were dommed anyway and Sophia was on board too.