Well, I've finally finished reading the thread and my opinion has remained unswayed from my original position.
My "canon" Warden is a human mage (female) who survived slaying the archdemon through the Dark Ritual. (She didn't want to die, nor was she willing to sacrifice her lover's life either. HOWEVER, had Morgana not been the Warden's companion throughout the Blight then the Warden would have instead chosen to sacrifice herself instead of trusting the witch.) She considers herself to be fairly level headed and practical and although she thinks that the Chant of Light is the most beautiful thing she's ever heard, "True Faith" escapes her. For what it's worth, she personally doesn't believe that the Seventh Blight will be the last either as the "Old Gods Theory" just doesn't ring quite true to her. (She also has some serious questions about the actual mechanics behind the "Grey Warden Death Blow", especially considering the "messiness" that spirit possession brings to the "Two Souls/One Body" Theory.)
She allowed Avernus to live and continue his research because she knew that if he was faced with a choice between saving the Darkspawn or Humanity he'd fall on the side of Humanity. The fact that his research is showing promising results in the war against the Darkspawn makes the choice to look the other way at some of his methods easier as well.
She killed the Architect without a second thought for what amounts to the same line of reasoning, in said choice she knows that the Architect would pick saving the Darkspawn over Humanity and that makes him too dangerous to be allowed to live. Of course the fact that his conduct has threatened the people under the Warden-Commander's charge made the decision a easy one to make.