Funny how I find interesting threads when they're already pages long. Anyway, my two cents.
I think Loghain used the Grey Wardens as an excuse to secure Ferelden. Given his background as a liberator and hero, he must have been appalled to hear that Cailan was to use Orlesian troops against the Darkspawn. Maybe abandoning Cailan was a little too harsh and somewhat cruel but if you try to see from Loghain's point of view, it was the only way to fend off the Orlesians (strategically, it was almost flawless - if the Warden and Alistair didn't survive, that is).
Also, he was far from paranoid: anybody who played Return To Ostagar DLC knows that Cailan was going to, err, dump Anora in favor of the Orlesian Empress. Keep in mind Loghain was also the Queen's father, no wonder he'd go to any length to protect Anora.
Loghain, imho, was never the villain in DA:O. He seized the opportunity to protect Ferelden the best way he could. True, without the Wardens he would have never stopped the Blight, but you can't blame him over the Wardens being a secretive lot. Eamon was already putting Cailan against the Mac Tir. In a twisted way (slavery, poisoning, relying on Howe), he was going for Ferelden's independence.
Honestly, Cailan was a fool and nothing in my 17 playthroughs convinced me that Alistair would be a better asset (perhaps with Anora, but alone... Nope, he's clueless, Eamon's puppet like Loghain predicted). Even hardened, he's a whiny brat.
It might be hard to see Loghain's stance but, all things considered, sparing him and have him protect his beloved Ferelden is my personal "canon" every time I play through Origins. There wouldn't be a Fereldan country to defend without Loghain - and Maric -, his past glory makes up for his late mistakes.
Now, Anders. Turning upside down my reasoning on Loghain, he has nothing to offset his act. He was a good Warden but that's pretty much it. All his narrow mind can come up with are mages. He doesn't see anything else beyond mages and templars. Common folks? Bystanders? Civil war? The Divine issuing Rights of Annulment like candies? Or, the Qunari exploiting the chaos to strike again? God, he's just a pathetic idiot. He isn't even an anarchist, he doesn't care about "normal" politicians who agree to be manipulated by the Chantry. Anders/Justice's world is black or white. No compromise. Fair enough, not even my Murder Knife likes a compromise of sorts

Plus, he's unstoppable in his intent, plot-shield is silly when you already know he's up to something fishy (unlike Loghain when you first meet him at Ostagar. Partial about Cailan, maybe, but not outright suspicious).