1. Alot of anti-mage people seem to be under the impression that abominations are common, but they aren't. In lore and gameplay we get abominations out of 3 different ways: a: The mage is fleeing and is cornered into a life or death situation (usually with templars) and uses it as a last resort (By far the most common) b. The mage is poorly trained or not trained at all (as in Conner and Merideth's sister) and therefore don't have the discipline to resist c. Someone who is already an abomination forces it on them. (As is what happened in the Fereldan Circle)
That's it, If you properly train the mages, show common decency, but remain vigilant against the bad apples then you've solved at least 95% of the problem.
2. Do you mean how do they find mage's in general or how do they find rouge mages? For the first, the same way they always have: someone uses magic and it's reported.
3. Respond to what? A mage going rogue? Going insane? Should they escape from the Circle, it's a simple matter of tracking them back down with their phylacteries, in the unlikely case of one of the free mages going crazy I suggested Templar outposts, if these outposts have Sendings (used in Asunder) they can communicate with each other and track the rogue down relatively easily.
4. Again...why do you think the mage will suddenly just turn into an abomination? The only really I could see that happening is if the village got their mob on and decided to roast the poor fellow and proper training and education (both to the masses and mage) could reduce this likelyhood even further.
5. For some reason you seem to be under the mistaken impression that all mages have easy access to blood mage and a complete lack of morals. (In the first game the only way to learn it was from a demon).
1) Naive. Mages turn to abominations for all sorts of reasons.
Despair and desire come with life, and no amount of education - even assuming it's perfect - will change that.
I don't know where you got the 95% figure, but it's laughable.
2) And by the time the report comes (IF the report comes at all...the mage in question could easily leave no witnesses or use blood magic to convince the victim to stay quiet) the mage is in another country
3) Only the circles have sending stones.
With travel between towns taking days/weeks, trying to hunt down or police mages spread over a large area is a logistical nightmare.
4) Again the silly notion that mages only become abominations if someone attacks/forces them. That notion is proved wrong.
Mages can fall to either forced possession from a demon or they can be tricked to give in for various reasons. Connor only wanted to make his mother happy, there was no angry mob after him. Uldred, an educated mage, fell victim to his pride.
5) Actually, they do. Any mage can learn blood magic from demons, and demons are willing to teach it. Mages can go actively looking for demon teachers every time they dream if they so want.
In case it does happen, Templar Outposts should be able to detect this kind of thing and counter it within a reasonable time frame and if a mage does rise to some form of leadership legitimately it wouldn't necessarily mean a "new Tevinter Imperium".
You didn't explain how they would detect it or counter it.
6. Education is the only way to prevent those kinds of things. The Chantry will have to work at getting rid of the bias that's been spread around, but it'll take time. One thing that they'll likely have going for them is that this war might wipe out the bulk of the fanatics on both sides of the fence leaving some more moderate being leading both sides.
Biggest problem in your reply is right here.
No amount of education will change anything.
It's a matter of survival and self-perservation, and bias is natural, not some Chantry dogma.