I've been thinking more about what Sam said to Cas about his possession and I think it adds another, rather terrifying, layer to his experience.
Sam felt a presence - felt that he wasn't alone. Knowing what Sam had been through with Lucifer it must have been absolutely terrifying to feel like someone else what sharing your "housing". Added to that, Sam wasn't able to talk to Dean about it. Whenever it was brought up Dean diverted his attention. Dean had his reasons of course, but Sam didn't know that. He must have felt like he was going a little crazy - losing time, feeling like he's not alone in his own body. The fact that he's been "crazy" before meant that he's had experience with ignoring it. Which he obviously did.
I wonder why it's taken them until episode 21 to give us that bit of information. I realise that that scene existed mostly for us to start to see that Gadreel could be persuaded to double cross Metatron (and if it was purely
for that then I will want to join the indignation some have felt in that scene), but I would truly like to believe they were giving us more insight into what Sam experienced, which might hopefully play out later in the season (shut up! I can hope!).
ETA: Flisties are right! It was retcon so...BOO - ignore that stuff above. :(( *sobs quietly*
ETA ETA: After bouncing back and forth between thoughts offered in the comments I'm back to trusting my first instinct. Mostly, it's canon now so we can take from it what we want (or need). :)
There's also another factor in play I think.
We're seeing the battle between what's considered "good" with what is "right". Dean said he felt calm with the Blade in his hand. A good feeling no doubt. Gadreel possessed Sam with good intentions - heal Sam and begin his journey to be understood. Dean agreed to the possession with good intentions - save Sam. Sam has known what it's like to become powerful, with the good intention of revenging Dean. Cas definitely knows what it's like to want power for the "good" of Heaven. Even way back to Mary agreeing to barter one of her children for John's life - it was a good intention.
We might be left to question if something is considered "good" does it make it right? Even if Gadreel turns out to be misunderstood, an angel seeking redemption with good intention does that make what he did to Sam, Dean and Kevin right? Does Dean allowing Sam to be possessed without consent make it right because it was done with good intent? Does Dean holding the Blade to seek calm make it right? My answer is no to all those things, but maybe it's not as easy as that. Can I dare hope that maybe there's a lesson here in the Winchester world after all? That Carver might indeed have a (cunning) plan in mind when he opened this massive can of worms in 9.01?
I've said to a few that I will reserve my overall judgement of this season after the final frame of S9. I don't expect we'll have all the answers but I am hoping we'll at least see why
Carver opened this season with such a divisive, shocking and thought provoking scenario.