i was rewatching the end of 10x22 and realised something about the final scene between cas and dean. when cas says "i don't want to have to hurt you" to dean, dean scoffs, gives cas a sound beating, then turns to walk away. but then. cas says the colette parallel: "dean. stop." and i cannot get over the way this impacts dean.
cas has no idea what his words mean. he was not there with cain in 9x11 when he told dean the story of his wife. only crowley was there, and it's not like he's going to share any of this information with cas. so when cas asks dean to stop, he's not saying it in the hopes that dean will remember what cain said and be moved by that. he's only asking, in the most heartbreakingly gentle voice, for dean to stop. to walk away from this path that will lead him into darkness. and the only reason he's saying it is out of his love for dean.
but DEAN. dean knows the story behind that word. he knows that "stop" was what cain's wife, who loved him unconditionally, who forgave him, said in an attempt to save him. to dean, this would sound like an expression of love.
i think this is why dean walks back toward cas and hurts him so much more violently than he did the first time and then tries to kill him. because he understood cas' words through the lens of unconditional love and devotion. and maybe he realised that he also loved cas enough that he would stop if cas asked him. and the mark couldn't allow that - the mark was driving dean to kill anything that stood in his way, and while it didn't interpret cas, an angelic warrior, as a threat, a loving, forgiving cas brokenly asking dean to stop - that was a threat.
look at dean's eyes here. he was on the verge of leaving, he was walking away because he didn't think cas could physically do anything to stop him. but when cas simply asks him to stop, he turns back. he realises that, if cas begged him, then he would stop, that the part of him still clinging to humanity loves cas enough to do that. and that love frightens the part of him that has been taken over by the mark. so the only solution is to kill cas, to remove someone who could actually stand in his way.
and during this second beating, the most gentle of supernatural's themes, the jay gruska dean's family dedication theme, is playing in the background - it starts right after cas asks dean to stop. the theme that specifically reveals dean's gentler, loving inner self - that's the theme they chose to play while he's trying to kill cas.
but of course, in the end, despite what the mark wants, despite it seeing cas and his love for dean, as a threat, it still cannot make dean kill cas.
