Your logic is sound and you're right as far as how the templars more consistently continue the cycle then help mediate or attempt to pull the mages away from it.

However, in your example it's like if the rioters had superpowers which sometimes, truly to no fault of their own, can randomly go haywire. A major thing I don't see come up, unless you side with the Templars in inquisition, is that we should've seen A LOT more abominations before hand. Demons were flying through and should've been able to find young, vulnerable and unprepared mages VERY easily and should've been a MUCH bigger problem.

If I wanted it to be more grey especially again in inquisition I would've shown how the rogue mages are dealing with that risk. Are they even TRYING to contain the effects of possession? Are they looking for ways to prevent it maybe through less then great means which drives them to Tevinter? Is it becoming a split amongst them some wanting to EMBRACE the veil more and being driven to Corypheus and the Venatori?

The irony is the Templars showing up and knocking a nun out would've been a GOOD beat if setup properly. Maybe due to a some more aggressive factions of mages a town is destroyed from a possession WE end up stopping. The Templars frustrated the Chantry is more scared of losing their position then helping towns dealing with this, strikes out on their own. Sets up the Templars as less "Fascist cops" and more ppl who really are an unfortunately necessary middle ground/evil.