Hmm, but then again the Templar Order: Traditional Role codex entry says
In reality, the Chantry's militant arm looks first for skilled warriors with unshakable faith in the Maker, with a flawless moral center as a secondary concern. Templars must carry out their duty with an emotional distance, and the Order of Templars prefers soldiers with religious fervor and absolute loyalty over paragons of virtue who might question orders when it comes time to make difficult choices.
So maybe a mass Tranquilization wouldn't have such a poor turnabout? I imagine the issues would be more in getting enough spirits to cooperate, making sure these spirits are not corrupted into demons in the act of possession, and the emotional recoil in the reversion process, which would have to make this a very gradual and calculated process so we don't end up with even worse results than we started out with.
I have a hard time believing they were doing a very good job at identifying unshakable faith in the Maker when they failed so miserably at a flawless moral center. Faith is expressed through behavior, and the rampant abuses of mages and tranquil (remember even Minaeve comments on this, and she likes Templars) suggest they only looked for loyalty to the Chantry, a very different thing from faith. People with unshakable faith do not abuse their charges, or cover up abuses or indirectly condone abuses.
Unfortunately, they haven't made it clear whether the harsh conditions in mage circles such as Kirkwall's and Kinloch Hold were typical or what Viv describes is more typical. There was no question about the restrictions in the original DAO. Marriage in theory only, no children, no family, extremely difficult to get permission to leave the circle and only for limited times, Templars with absolute authority (remember Greagoir was ready to punish a warden mage even if he or she acted strictly under Irving's orders), no contact with birth families, etc. I have a hard time believing what Viv described was more typical considering the number of stories from other circles (for all we know, her relative freedom was largely the result of being a duke's mistress, not an option available or acceptable to a lot of people.)
Viv worries me a lot more as divine than Leliana. I see her leading toward Tevinter style mage rule, honestly. Cass is my first choice as a middle ground, but softened Lel is still a good choice (we don't know if she really was touched by the Maker back at the start of the blight, so maybe she's his choice
.) Her faith is certainly a lot more apparent than Viv's.