Remember last season when Dean blatantly refused to fight Lucifer when he was possessing Cas because he couldn’t bear to hurt him or destroy his vessel?
Now fast forward to Vince Vincente and how Dean told Sam ‘You didn’t expect Vince to survive’. Dean cares about people; he’s a good person, but he knows that being Lucifer’s vessel destroys the person. YET he refused to let that happen to Cas:
Yeah, that’s all, bye~