I think I know what you mean about him seeming like he's acting morally superior. For instance, when you meet him, he talks about Wardens as being able to inspire. Considering that he's acting like he's a Warden, that makes it look like he's talking about himself being an inspiration, which makes him seem full of himself! The thing is, when revisiting these scenes later, knowing the truth, I get a totally different message. He is talking about himself being inspired by Wardens, not being an inspirational Warden. He's telling the truth, but in a way that comes out wrong because of his overall deception.
I think that's part of it, but I also think that he presents a very strong image of moral certainty. He doesn't present as a guy trying to improve himself, trying to live up to something (which would have been easy as a Grey Warden considering the Inquisitor brings up the fact many Wardens have troubled pasts). He presents as very sure of himself. I'm sure part of it is, as you say, an unfortunate end result of his attempting to portray the Wardens as inspirational, but it's still a part of why I reacted as negatively as I did to discovering his persona was fictitious.
That surety is also present in his original plan to take Blackwall's identity: he presumes that he is capable of being that beacon of inspiration and that he has the right to make that choice. And perhaps he was correct on both counts, but again, part of my emotional reaction was based on the conflict of that morally certain man he presented as vs the truth of his crimes and just...the way he seemed to genuinely believe that his actions as "Blackwall" counted as atonement in any way rather than the luckiest break in the world. Which, to be fair, may well be something on which some fellow forum posters and I disagree. 
An interesting thing about Rainier's deception is that, once he lets you believe he's a Warden, once that untruth is accepted, he actually almost never lies. If you straight-up ask him questions that he can't evade, where telling the truth would reveal his secret (and thus stop him from doing what he sees as good), he lies - but otherwise he actually tries to tell the truth in a way that's compatible both with his old experiences and with the life he's trying to live now. I noticed this frequently when replaying the game.
But Warden stuff does make up a significant about of your conversation. And while it's great that he may have tried not to actively misrepresent his views of the world, it doesn't change the fact he repeatedly misled the Inquisition with regard to important, pertinent information, including the very reason he was recruited in the first place.
You go looking for him because all the Wardens have disappeared and that's weird. You find him and he says he has no idea where they've gone but he doesn't want people to think they've been abandoned by them and so he'll join the Inquisition. Which sounds honourable and all, but if he'd been a real Grey Warden then either we'd have found him and he'd be experiencing the False Calling and could tell us about it and maybe we could have stopped the fiasco at Adamant sooner. Or he wouldn't have been there to find and maybe we'd've kept looking into the mysterious disappearance and again, perhaps we would have been able to stop Clarel before things escalated as terribly as they did. Or maybe it would have made no difference, but we'll never know.
Blackwall was asked his opinion on Corypheus' status as a darkspawn and how to kill an Archdemon because there was a possibility his dragon was one. He gave us incorrect information. What if it HAD been an Archdemon and we'd merrily sent Blackwall on his way to deliver the killing stroke?
He may have been well-meaning but bad intelligence is more dangerous than no intelligence. Just because you mean well doesn't mean you aren't capable of making a situation worse. Or that you shouldn't be smart enough to realise that's what you're doing.
I disagree. I think that he wanted the real Blackwall's sacrifice to not be wasted. There might have been an element of self-preservation, but I really think that he was so transformed by Blackwall's lack of self-preservation that it couldn't have mattered much. The main thing was wanting a better man than he was to be alive, wanting the worse man to have died. He couldn't know if the Wardens would take his word at having been recruited - after all, couldn't any criminal show up and say that a Warden who's now conveniently dead had recruited them? - so he saw the deception as his only option.
Perhaps but as I said, what he wanted and what he did don't necessarily add up. If he was lacking in self-preservation and genuinely remorseful then he should have presented to the Grey Wardens as a recruit and told them what happened to Blackwall. The Wardens deserved to know that Blackwall was dead. If they blamed Rainier for his death, well, frankly, he would have been accused of a crime of lesser magnitude than the one he actually committed. If they didn't want him? Well, he was given a chance to atone by becoming a Grey Warden, but Blackwall's offer wasn't an inalienable right. If they turned him down, he's stuck in the bed he made for himself.
He had the opportunity to genuinely turn over a new leaf based on Blackwall's inspiring death, and instead he chose deception. Even if I accept it as complete coincidence that this option also happened to be the one that kept his own neck safest (and I actually agree that he - at least consciously - believed it was coincidence), who is he to decide that he has the right to do this? That he knows what Blackwall's death could or should mean? He's going around representing an Order he's not a member of and without their permission with no idea what the repercussions might be.
Are his intentions good? Probably yes. Did he achieve some good stuff? From what we saw, also yes. But there's an arrogance to his presumption that annoys me, and as I said before, good intentions don't mean you're not making a mess for someone somewhere. Frankly, if he wants me to believe that he was trying to atone, I want to know why he never submitted himself for judgement to anyone, not even the Wardens, whom he professes to respect so much.
I suppose the bottom line is, he did something so awful, I don't think he should get to choose his own punishment. Which again goes back to explaining my bitter emotional reaction to him, I suppose.
When he decided to "become" Blackwall, he clearly didn't know anything about any of the negative aspects of being a Warden. This is just the same as the protagonist of DA:O. You are sent to get darkspawn blood, but you don't know that you're going to be forced to drink it, don't know you're going to be tainted, don't know about the Calling, or any of those downsides. And, if you see the lack of knowledge that Blackwall displays in several conversations, it's clear that there are still plenty of things that he isn't aware of, e.g. the Ultimate Sacrifice. He wasn't trying to evade the negative aspects because he literally didn't know about them.
Sure, I agree initially. But in the interim he either found out, or he didn't.
If he found out, then he's aware quite how inauthentic his repentence by living as a Warden is. If he didn't then, as I said, is he out there using Warden treaties he somehow got hold of, recruiting people with no idea what he's asking of them. I know that recruits aren't told, but the people recruiting them know and certainly consider this before asking them.
Regarding his general ignorance of things like how to kill an Archdemon, well, I already spoke about how that is potentially endangering to the Inquisition and it's reckless of him to act like he has information that's pertinent to an imminent threat when he doesn't have it.
As to not attempting to evade the negative consequences, we get back to my perceptions of his arrogance in assuming he was in a position where he could make the decision to become Blackwall. He might not have intended to evade it, but he did. Just because he thought he was going to be allowed to repent by being a regular soldier type guy doesn't mean that was actually the deal. It gets back to people not being allowed to pick their own punishment for serious crimes.
Actually, I think that his hatred of the Orlesian upper classes partially comes from hating the person he used to be, particularly how he let himself be a tool in the Great Game. Is it hypocritical if you recognise your mistakes and move away from them?
I completely agree. That's why I mentioned that the hypocrisy might be based in self-loathing. But I do feel it's still hypocrisy because he encourages the belief that he would never have anything to do with anything like that, rather than presenting as a man who realised it was all awful and left it behind. It's less like he's recognising his mistakes and more like he's pretending he never had them. Or at least hoping we'll think of him that way.
Under normal circumstances, that'd just be an irritating character trait, but in context, it's one more thing that paints me a picture of Thom Rainier as a guy who genuinely wants forgiveness and redemption but has too much arrogance and ego to ever let himself stop being the protagonist. Even when he finally gives himself up, it's still about what he wants, what he thinks is right.
I actually agree with you here. While I believe in the power of redemption and defend the reformed Rainier/Blackwall, I absolutely think that his original crimes were abhorrent and would never try to excuse them. None of the people whose deaths he caused will ever get the second chance that he did.
I don't feel like his men can be excused either. It makes me very uncomfortable not knowing what happens with/to the guy that Blackwall saves from being hanged. I kinda feel like I should at least try to find a place for the guy in the Inquisition, given that I do that for Blackwall... but then again, I don't know how repentant this guy is. I wish there was an option to at least discuss it.
Yeah, I think we're in agreement here!