Everyone has reasons for doing "evil" things. Must you be some cackling one-dimensional character with no motivation besides doing evil things for the sake of being evil to be evil yourself?
I don't see people defend Corypheus in DA:I, because his actions are done out of pride, yet much sympathy for Calpernia for example. The only real difference between them is Calpernia does evil things for other (Tevinter) people more than just herself. Corypheus is prideful, but so is Loghain. Loghain's actions (post-Ostagar at least) are done because of his massive ego, presumably for the people, which conveniently included preserving his own life at any cost.
It's funny how people defend evil actions when they're done supposedly not just for yourself. You'd never know Loghain was fighting for the people though based on his actions.
...About Ostagar... I'm no military strategist, but even if that battle was (debatably) doomed to overall fail, wouldn't it have been better to fight to the last man to severely cripple the horde than let it march undeterred throughout southern Ferelden? How was Cailan wrong for trying to neutralize the blight's teeth quickly? He was a fool in many ways it seems, but even a broken clock is right twice a day. It seemed in this case he had the right idea. Could he not wait for reinforcements before the horde marched on or was he just impatient because of his visions of glory? It sounded like Loghain's fear of Orlais, possible sabotage of the battle, poisoning of Eamon beforehand, low opinion of Cailan, belief this wasn't a blight, abandonment of his king, etc. only made the battle worse. Clarification would be nice.