The matter of spirits and demons is one that Lavellan leaves to Solas, deferring to an expert who's knowledge she's learning firsthand but can never hope to match at present. Maybe if she had a decade or two to devote to it, much like he must have. But at least Miles seems to be interested, rather than insulting them and the world by turn.

"To use magic, one must have the willpower to both pull magic through the Veil that separates the Fade from this world, and to resist the whispers of any demon bent on possessing them." It's an occupational hazard, if one will.