I never excused Loghain's actions. I just said his actions are more understandable because at least he didn't do it for personal gain, unlike Rainier who did what he did for a handout. I execute Loghain for his crimes, and would leave Rainier to the same fate if it wasn't for the fact that is what he wants. So any hypocrisy you see is not there.
Some of the things you recover are Warden scrolls, so it is most likely a combination of both.
I didn't get that quest since I didn't romance him.
Do tell me how you really know that some part of it wasn't for personal gain? Just because Loghain said something doesn't make it so, although I was willing to take the man at his word about some of the things he said on the one occasion that I spared him - but then I'm capable of giving people the benefit of the doubt on occasion.
At least in Blackwall's case, aside from my heart and the evidence in front of me, I had my trusty spirt-human-lie detector with me (aka Cole). You say you can understand about Loghain's actions, well what's the problem in understanding Blackwall's actions? We know what he did and why; it is also understandable, just like the actions that Loghain took.
It's just not necessarily something that's forgivable, depending on your moral stance about situations like this. Oh right, the scrolls...yes, well there was plenty of time to read them, and if that was actually what he was after (knowledge for the sake of posing better as a Warden), then he sure did a p----poor job of it, seeing as he gave himself away repeatedly. With the amount of time that passes in the game, I'm sure he could have read all them by the time I started asking him about Warden-related issues.