Okay, first, yes, Castiel’s mission was him being employed as a soldier as opposed to some sort of compassionate salvation at first, but he definitely grasped the other, kinder reasons for saving him in a way none of the other angels ever have. “I’d give anything not to have you do this,” etc. “I don’t envy the weight on your shoulders”, “It’s not blame that falls on you, Dean, it’s fate.” etc. etc. etc. etc. Castiel also—this is indisputable canon—had no idea what the fuck was going to happen when he did so, or for twenty episodes afterward. He knew Dean was going to help humanity (as he was told repeatedly cos that was his near entire reason for helping the angels), that he was “different” somehow, but he did not know how. (Also, letting Sam out was after Naomi-esque LITERAL RESETTING OF HIS MIND, literal resetting with the drill akin to S8.)
I want to point one thing out that I think is a large divergence in post-S6 Cas-fans and Cas-haters: how much we accept the characterization, the actions, that are meant to vilify characters who aren’t villains (or offer some sort of “Good” to villains who haven’t changed), as part of who they are instead of fascinating and dramatically necessary flukes, things they wouldn’t do unless they were forced into mental, physical, or situational corners, things that are purposeful and out-of-place that are meant to make you hate Castiel and characters like him so they can kill them off with minimum uproar. People who are already so inclined find this believable and accurate and hate him easily; people who are skeptical or inclined to like characters that aren’t the brothers are like “this was a really shitty terribly written purposeful vilification so they could kill him off” and don’t just swallow the muckraking over Cas’s cohesive character as established, thus far and afterward, they did.
Castiel getting Sam out of LUCIFER’S CAGE without a garrison makes…y’know, no sense????????? None. And it was an afterthought of a plot point, which means that all that “lying” was literally just ret-conning: Misha played it fucking straight because Castiel really didn’t know. As zatnikatel pointed out in an Ask with me last night, why the fuck would the Seals exist if the Cage could be so easily “harrowed”? Why would Zachariah or Raphael or Michael not have just y’know grabbed Lucifer from the Cage for the big archangel fight? And why would Cas—who is shown at least thrice during that season to fucking suck at outright lying—be super goddamn confused about Sam’s soul but determined to find out more, then super concerned about Sam’s soul deteriorating his body, then completely cold about near-KILLING him by breaking the Wall. Why would Cas, who fucking adores Dean and is one of the only characters to validate his feelings 99% of the time, snark at a shit-scared best friend when Dean asks for help with Sam? Soulless Sam’s mistake as a plot point, the whole thing, made no sense for Castiel, and anybody who doesn’t already want to hate him caught that.
That aside, it did happen, of course, it is canon by some definition, but it’s shitty-ass canon they’ve tried their damnedest to undo, by showing Castiel’s debilitatingly depressed remorse and frequent attempts to make amends to both Heaven and his earthly family, his SUICIDAL need to punish himself for it, by showing how hard Cas balks from ever again being a leader (again—way more in line with his character without Crowley’s influence or the literal bodily-control of angels or monstrous SENTIENT souls), how Castiel was convinced enough of his own Badness for a demon to convince him she was trustworthy when she was “working on him”, that they’re somewhat the ~same~ and she feels his thorny pain, how much he loathes Crowley now that he’s out of the “I’ve got the hookup” mental woods, how Castiel is terrified of/morally opposed to ever endangering any human or angel again with his direct or indirect actions—even for a victory or survival. By “nothing is worth losing you” and “you gave up your army for one man”.
Like, fuck off if you think Castiel is the same as that. “Who I was, what I did, is not who I am.” he says outright to Bartholomew. This whole season was a lesson in Castiel’s development into a person who would kill Godstiel rather than endanger humanity/angels if he had the chance to do it over again, because he cares that much about that—which cooperates way, way better with his established characterization in every season, as I’m sure Carver knows. This whole season was a lesson in “sorry for everything in S6-S7” over and over and over again.
Also the last part, THE LAST PART, I’m GOING TO HAVE TO RING THE BULLSHIT ALARM ON THAT. I COUNTED. CASTIEL EXPRESSED REMORSE IN VARIOUS WAYS INCLUDING AT LEAST FIVE OUTRIGHT VERBATIM ‘I’M SORRY’S NINE FUCKING TIMES BEFORE THE END OF S7 ALONE. “He never apologized for either.” BULLSHIT. BULLSHIT. BULLSHIT. BULLSHIT. BULLSHIT. BULLSHIT. NINE FUCKING TIMES IN THOSE TWO SEASONS ALONE, BEFORE, DURING, AND AFTER. He’s apologized to Dean, and Sam, multiple times, and probably angels? Yeah, I think angels too, but please correct me if I’m wrong (though honestly the angels are the ones he owes the least to: killing them in S7 was genocide to PREVENT genocide, and they have abused/tortured him literally since at least Lucifer’s departure—he killed them to survive exerting choice long enough to protect humanity?).