So Supernatural was on last night, which means time for the weekly round of "who's the biggest jerk and why, and who owes what to who..." Since I’ve been reading a lot about it, I'm going to say ...
...why I think I think Castiel's transgressions coming to light is irrelevant. Possibly spoilers to follow.
So the problem with Castiel is that when people get annoyed at his behavior, the answer is: he's an angel. And the answer to that is: So what? Which is not really something one can argue with because it's basically valid. But since I've seen numerous posts and fandomsecrets in the past few weeks about how people don't understand how the characters, particularly Dean, don't see it this way (how can Dean call him a friend?), here's how I read the saga of Castiel.
He's an angel. I know: that doesn't absolve him. But angels are something that comes up a lot in my RL (angels as a subject, not as a personal spiritual experience), so it's hard for me not to see that as a really fundamental thing. Someone mentioned in a discussion that angels were "supposed to be better than we are." This is really not true. According to Christianity (and this is not meant to be me telling any Christians reading how they think, just that this is Christianity as it's always been taught to me), good=God's will. Many Christians lay it out even more clearly: God gave us free will, and we must hand that free will over to God. Thinking for yourself about right and wrong is not what you're supposed to be doing. (You're human and so will utterly fail at it.) You're supposed to do what God wants you to do. He knows best even when it looks to you like he doesn't.
Angels aren't better than humans, because they don't have the same struggle about following God's will. But that's still what they understand as good. SPN isn't a strictly Christian show by any means, but this aspect of being an angel is clearly present. Castiel didn't spend last season trying to figure out the best thing to do, he spent it battling a growing impulse to commit the worst blasphemy/crime/transgression he could ever imagine in thousands of years of life. Other angels had made the same choice, of course--Anna is an obvious one. But it was a *big choice.* One probably on the level of risking the belief that gravity doesn't exist. Sure he knew Anna did it, but that's about as comforting as knowing Charles Manson did something. Anna's not a role model, she's a cautionary tale.
And Dean *knows this.* He knew it all last season. He also felt--correctly, imo--that Castiel liked him personally. He grew to like Castiel personally in return. But he was always aware that Castiel was not on his side, but the angels. He saw Castiel's doubts. He saw him sneakily help Dean out through a loophole. But the only time Castiel was ever seriously considering taking that walk off a cliff was when he was going to tell Dean about the angel's real plan, which Castiel knew. And then he got yanked back and returned more committed to the angels than ever. Some have suggested there was torture involved here-I doubt it. Torture wouldn't help. What they'd need to do was re-convince Castiel of everything he's known was right his whole life. Yes, he had reason now to doubt God was even giving the orders, but he'd also always taken orders from other angels. He wasn't an angel of the presence to begin with. To consider trusting himself or listening to humans is a hugely different thing than sticking with the angels.
So he comes back recommitted to the angels, and Dean knows this. In the scene where Dean's in the magic room, being kept from stopping Sam from killing Lilith, Castiel is one of the people keeping him there. Here is where Dean learns the angels' plan. He learns without a doubt that the angels want to bring Lucifer back and want Sam to do it. And Castiel *defends* this plan. He defends the angel's pov as his own--why would you not want paradise? It's a GOOD THING for Sam to do this. That's why Dean has to argue back the human pov. Or at least his own pov. Because there are a lot of Christians who would enthusiastically agree with Castiel and are eagerly awaiting Armageddon as we speak. If you took this situation out of context and ran it by people, plenty of religious ones would side with Castiel.
It's only in that scene, in response to Dean's arguments, that Castiel actually changes sides. This does not mean that Castiel isn't culpable for everything he did before. The fact that he was following orders doesn't mean he didn't do them. It's just not a big dirty secret to anybody that he did that. I don't think he's ashamed of it either. Does Dean know that Castiel let Sam out of the panic room? He's never said so, but I don't see why he wouldn't consider it a possibility. He knows a demon couldn't do it, right? He knows that angels were manipulating events to make sure Sam killed Lilith. He faced Castiel in the angel room when he was being kept from stopping Sam, which is practically the same situation as the one in the panic room, and Castiel told him to let it happen. (Nice parallel there: Castiel opens doors twice, for the opposite reasons.) Even if Castiel hadn't used his hand to open the door, he would have supported anybody who did. Just as he wouldn't question an angel asking him to help out in smiting a town or killing a firstborn. Even if Sam and Dean do consider Sam’s release from the room at that point their downfall (which I don't think they do) I would be surprised if they were all that shocked that Castiel had a hand in it.
So he made the big decision to side with Dean. To stop Lucifer rising. So he lets Dean out and...it turns out making your own choices is even more confusing than Castiel imagined! When you follow God's lead, things turn out just the way God says they will. Or even better, you don't have to think about it. God doesn't have to share why he's doing anything. Nor do the angels. You're just always right because you're doing the will of God or his agents. But listening to Dean didn't even lead to the goal Castiel thought he was choosing, because Dean didn't get there in time. There's even more risk and chaos than Castiel thought.
People get angry when Castiel is all, "I gave up everything and you didn't stop the apocalypse!" and "We can't take a chance on this kid making the right choice--Sam didn't!" and I get why, I just don't think any of the characters-including Castiel--are as invested in the "who's fault was what and who's partially to blame for who because if you hadn't done this I couldn't have done that..." They're only all obsessed with their personal issues. Dean was focused on Sam's sneaking around with Ruby and leaving with her when Dean gave him an ultimatum because it was personally hurtful to Dean and made him feel insecure, not because that made it Sam's sole fault the apocalypse started. Sam's obsessed with his drinking demon blood and going with Ruby because he feels guilty and responsible for the way it turned out and his feelings at the time. Dean was obsessed with breaking in hell because he felt guilty and responsible for the result of his actions, both those he knew about at the time and those he didn’t. (It probably makes Sam's actions all the more painful since if Dean had been able to stop him he might have done something to right things after his own actions.)
Castiel just knows he stepped off a cliff and is falling through the air, more out of control than ever. I know plenty of people have no sympathy on this, seeing no reason to judge Castiel's actions differently just because he wasn't human or just because he had thousands of years of not considering the consequences of his own actions. He still screwed up in human terms. But if you flip that around, Castiel probably equally doesn't give a damn that Sam and Dean are human because they still screwed up on divine terms. And he still doesn't think the concept of destroying the world to bring paradise is necessarily nuts. Whether or not we consider Castiel being an angel an excuse, he's not going to stop being an angel. When Castiel says "you didn't" to Sam regarding making bad choices, I don't think he's joining in the fandom debates about whose fault everything is. I think he's just flatly stating that trusting the wildcards that are humans is just far too risky. You really want to stick with absolutes as much as possible: angels, demons, God. He's trying to bring as much of the order of heaven into the world as he can, and he's failing. Sam and Dean are both too unpredictable. He's venting his anger at his situation at them too, but I don't think he's doing it on the same terms as viewers do. His issues with Sam are not, imo, what viewer's issues with Sam are.
Finally, SPN seems firmly on the side of those imperfect humans here. Castiel's plan of "let's kill the kid" wasn't an option. First Castiel's attitude and then Dean's fell away, until there was only Sam's plan that was even possible. I see how it can be frustrating to not just judge Castiel the way we would anyone else, I just don't think it's possibly to get much out of the character that way. It's just bound to be frustrating. I think Show has at least put work into reminding us that Castiel mindset is completely foreign and alone. It's not just about odd turns of phrase like "The voice says I'm almost out of minutes."