He could not leave until he had some excuse to hand his troops; would not be fitting the General. That is why the look of concern is so intense on the man at departure....
Ne sneers at Ser Cauthrian; not at the Darkspawn. Multiple witnesses, including some tortured for holding 'another version of the truth' state it clearly enough. Lore states it clearly enough. Etc.
Great man gone bad; normally lose him at the Landsmeet.
Few things, it's impossible to say what he was thinking at the exact moment he gave the order. Gaider did say that it was a split-second decision to retreat that he made as the beacon lit and that it wasn't pre-planned. If you don't want to take that, then we can just as easily say that Loghain's expression wasn't him sneering as he led a retreat but trying to hold it together and keep his composure, knowing full well what he was sacrificing, or something similar, and see a man who's torn about his decision. As Loghain tells Wynne, it wasn't just Cailan and the Wardens he was leaving behind, he had plenty of his own men down in that valley as well, and he knew their names and their families, and makes clear that he knew full well what he was giving up when he made that retreat. All we have on that moment is the devs word and the animation of him giving the order of his retreat, there is nothing there on his motivation. Merely us inferring it.
We are all entitled to our opinions, but I don't think that he wanted to give his men an excuse works in the game, especially given the context of everything else that does happen. What I mean is, Loghain is not and never was a simple character. He's a complex, well-rounded one. One torn by regret over a hard choice, but knowing full well that he would make it again. I love his dialogue with our companions, and his back and forth with Wynne in RtO.
The tortured nobles in Howe's dungeon in on Howe's head. Howe's actions are his own. There is no evidence linking Loghain to their torture and kidnapping, or approval of what Howe was doing. There's a reason at the Landsmeet that bringing up Howe isn't the most effective tactic. Sure, it helps with that young man's father speaking out and bringing in the state of his sons legs, but Loghain's response is just as valid. Howe's actions are his own and Loghain cannot be convicted for another man's actions.