Steve looked at the scars and winced just a little bit, imagining in his mind how that fight must have gone down. To be bitten... the fight he'd had with a vampire resulted in no bites to himself or to Andrew, although admittedly he didn't think the creature had really tried. It had seemed more possessive of its territory than actually out for a meal, if that's what they even called it.
But facing angels in battle? At that he felt a hesitation that had less to do with the strength of the opponent than the nature of the them. "Wait... are you telling me that angels would attack me- or us? Why?"
Well, maybe because he was healed by a demon. Maybe there was a great deal more to it all than he knew. If he was understanding Castiel correctly, he needed a knife and there was but one way to get it, and it was not a way that he was comfortable with. He'd never ask for one that belonged to another, but he doubted that he could take one for himself if what was required was what he thought he heard.
"If I understand you right, that's not something I can do. I don't want to kill anyone, not unless there's no last resort and it can't be helped." Demons were one thing, but angels? Completely different.