Because Meredith is perfectly fair and willing to listen to reason. She has never acted brashly or flagrantly ignored/neglected or permitted misconduct as it pertains to mages. She definitely hadn't already sent for the right of annulment and was for certain not dying to pin something on Orsino for the entirety of Act III.
Nah, if I were Orsino I would come running to Meredith with evidence of a blood mage.
Seems like a reasoneable choice(sarcasm) to me
This presupposes that Alistair thinks the Circle life in a sane circle is a terrible fate. Where does Alistair reflect this?
'Not in their best interests' is not the same as 'couldn't', you know.
Moreover, you are assuming the Grey Warden will view the mages the way you do. I see no reason why they should: the Wardens are a small elite force, not a mass-recruitment draftee army always claiming more. You could credibly claim that the Wardens would want to recruit more strong mages, but what about weak mages? Those they don't think could make the cut, or are succeptible? There would still be a reason to keep the Circle then, to train up new mages and keep the undesirable ones... even if we didn't consider the other costs of trying to abandon the Circle system.
1.
You might act as if you don´t know the fact, that Alistair grew up in Arl Eamons castle. As a former templer, he is well aware of the fact, that at some point Connor might be killed or made tranquill. He just wouldn´t take that chance. If Connor would have been at Fereldens circle, like he should have been as a mage(by chantry doctrine), he would have died in the purge. His mother realized him to be a mage befor the purge happened.
2.
I never said I´m assuming anything regarding the Wardens. Duncan( as the Warden later on in Denerim) clearly states, the Grey Wardens do and use anything to stop a blight and kill all darkspawn, even bloodmagic. That is why they would train every mage to be as powerful as possible, and kill those who are possessed.
Edit:
BTW: The Grey Wardens consider themselves to be an army, they just don´t have enough recruits