Castiel was having more than one doubt of his own, so many questions over whether this was the right thing to do. But Margareta had made her feelings very clear and now Castiel was bound by that.
"I am honoring her wishes, that's all I can do," he spoke back to Sam, his own voice lowered as well. "Whatever I want to do doesn't matter, I will not, I will never violate someone's wishes like that. She's not irrational, we've already spoken at length about this. I've tried to change her mind, believe me, but she's just as stubborn as Ruby herself."
He took a step back, looking at Sam even as he raised his voice slightly.