Cas returned the smile, albeit somewhat vacantly. The knowledge that Morpheus was at least willing to believe, despite being jaded made him feel...pleasant, for lack of a better term. Given the nature of belief among so many hunters, it was pleasing to find at least someone willing to try.
"You are right, it is difficult. But that doesn't mean it shouldn't be attempted. I...feel that my mate saved me in many ways. Had I resisted her, I doubt I would be here."
After all, angels had no sense of self-preservation. They were not created with it. Without someone to tell him when to stop, Cas had very nearly destroyed more than just his targets.