@Keroko: In my original playthru - I chose to enter the Fade as a mage and fight the demon. I don't read spoilers on a first playthru and I try to play the game as if I were actually the character - and I couldn't imagine just leaving the demon in there on the off chance I could go talk with some mages and maybe they could help me and I'd get back and the town would be a smoking crater.
For my Main Warden however - who cared nothing for the boy or his mewling mother - going to the tower was out of his way. Killing Isolde however required putting Morrigan in the Fade as my Warden was a fighter. Without metagaming - my Warden 1) Didn't want to risk his mage ally to demons. 2) Didn't completely know if he could trust Morrigan. and 3) Knew exactly two things about magic... Jack.. and Sh_t.
SO... instead of making a bigger mess - he just decided to kill the boy and be done with the whole thing. He doesn't sit in the blood laughing maniacally afterward... he doesn't twirl his mustache... he heals Eamon because he had already been to the Urn and had the ashes.
From a meta-point - I have to decide what my characters would do. Going to the Circle seems like a very naive, idealistic, risky maneuver even though I know it works... and I don't usually play a character who would take the lives of people and risk them like that.
Nor does saving Connor do anything personally for me meta-wise... I don't feel the same moral restrictions I do in the real world. And, of course, in the real world "meta-gaming" is impossible.