I fear we didn't talk enough about Cas's "I'm not going to let you or anyone hurt the people I love." And the murderous look in his eyes right after Donatello cursed Dean.
And there's something else in the script that's not exactly how the show presented: Donatello did mention that digging into his mind could fry them both, and Cas didn't care. We didn't really see how much he suffered, but in the script, it says: it's painful for him too, so much that Cas screamed.
Donatello: What are you going to do?
Castiel: Something I swore I'd never do to another human without their permission...
He unbuttons the cuffs of his shirt, rolls up his sleeves...
Castiel: I'm going to strip the spell from your mind. (beat) I'm sorry -- but I have to do this, because I know you cannot be saved --
Donatello: I don't want to be saved.
Cas nods, absorbing that --
Castiel: Then let's begin.
Donatello's mind races, trying to talk his way out of this --
Donatello: Unless -- we could work together!? My knowledge and your power? We could rebuild the world as God intended. That's what all you angels want, isn't it?
On Cas -- tempted? Not even close.
Castiel: That road... has evil ends.
Dontello's really panicking now.
Donatello: Wait --! (tapping his head) The power I've absorbed -- it'll fry us both.
Castiel: It might.
Donatello struggles in his restraints as -- Cas gently takes his head in his hands. Donatello's eyes roll back, Cas scanning his mind -- after a beat... the prophet begins to scream. An animalistic wail --
Undaunted, Cas tightens his grip. Focusing. Gritting his teeth. This is painful for him too. And then --
Cas starts to scream as well.
Cas could have fried himself... just because Donatello hurt the people he loves, because he hurt Dean, and Cas knows Dean is the people he loves, and he's not afraid to admit that to the prophet... But Dean doesn't know that. Dean doesn't even know how much risk Cas took or how much pain he endured (how much does it take to make an angel scream?) to get the spell for him, to open the door to the other Apocalypse world to get Mary and Jack back.
And why doesn't Cas care about his life? Oh the angel who only sees himself as a weapon -- we have that in the script but not exactly in the show as well:
INT./EXT. Impala - Night
Driving down a country road... Dean glances at Cas.
Dean: How you holding up?
Cas stares out the window, detached --
Castiel: I'm fine.
Dean: Look, man, think I can tell by now when something's botherin' you.
Cas relents, facing Dean. Admitting --
Castiel: Lucifer...
Dean: Yeah, I know how badly it burns you up we haven't been able to find him. I'm with you...
Castiel: It's not that -- (reconsidering) Well, it is that. But... I've been thinking... about the time Lucifer and I spent incarcerated together... (as he forms the thought) The only way I was able to outmaneuver him and escape was by trusting my instincts, relying on my angel nature, instead of pretending to be something I'm not...
He fall silent, but Dean presses --
Dean: Like what?
On Cas -- an answer, a realization hitting him. One he doesn't want to voice. Dean picks up on his hesitation --
Dean: What -- like us? Human?
Cas nods. On Dean -- as that lands. Cas pivots --
Castiel: Dean, I have to believe I was brought back for a reason --
Dean: You were. Jack brought you back 'cause we needed you back.
On Cas -- part of him agrees, but another part believes --
Castiel: I was created to be a soldier -- a weapon in the service of good.
Dean: Cas, you're more than a weapon --
Castiel: In times of peace I can be, but if Michael really is coming --
Dean: We'll figure it out. (beat) Don't take this on yourself... you don't have to.
Cas absorbs that, stone-faced -- as Dean pulls the Impala into a field.
The two of you really are the same... one thinking of himself as a weapon for Heaven, the other "Daddy's blunt instrument". And no matter how much they tell each other "you're more than a weapon", part of them still can't fully absorb that...
Dean's so soft and caring in this dialogue (probably exactly why they cut out the majority, leaving only the part he asked how Cas's doing, that they needed him back, which is just as sentimental as S08E17's "I need you").
If only they could really believe and absorb and understand how much that's true, how much they matter to each other. I think neither of them has enough of an idea how much they mean to each other... and that's the problem...