I know. With how hard it can be to identify abominations, you'd think it would be more secure to keep all the mages in an enclosure where they could be watched? Maybe a tower out on a lake? Maybe a ... circular building of some kind?
Might actually be a worthwhile argument if the Templars weren't already completely horrible at their job while the circle system was still intact. But they always sucked at their job.
In DA:O There is a demon infested Orphanage in the middle of Denerim and they sent one blind dude, who dies.
Also there is a huge blood mage hideout also in the middle of Denerim and they send one dude, who also dies.
And let's not forget that Jowan first esily escaped the Circle, the escapes again when they send one dude to recapture him, a known bloodmage, and Loghain bails him out and the one dude they send surprisingly not dies but just becomes a vegetable.
Also the Circle gest overrun by demons, most of the templars died/became possessed as well and they had to call reinforcements from Denerim (That probably wouldn't have helped either, since at this point I'm convinced the headquarter in Denerim would most likely decide to send just one dude
).
In DA2 it doesn't get better, As there are tons of bloodmages and even more demons running around outside the Circle while Merediths templars are apparently too busy beating up the mages that are already contained in their circle to do anything about it.
Their recruits get possessed by demons and nobody suspects that until one of them transforms into a demonic form right in front of Cullen.
The first enchanter is able to exchange letters with and bloodmage.
The blood mage mentioned above is investigated by .... you guessed it... one dude, who then dies.
Some of the templars actively work toghether with blood mages in Act 3, and then die while doing so.
And a whole bunch of blood mages escaped from the circle during the course of DA2.
And when an apostate mage/abomination blows up the chantry they decide to kill every mage, except the one that blew up the chantry, and some of the mages escape anyways.