Thanks for your comments & thoughts.
Just to be clear on my original question though ("Loghain’s behavior is not realistic") -- I meant to say that people like the Arl, the queen, and others that know Loghain say something like "I know Loghain, but that's not like him" or "why would he do something like that?"
Obviously with comments like this (from MANY of those that know & are close to him) -- something isn't right. As you dialogue with Alistair when taking the tower of Ostagar, there was a hint of an "inside job" regarding how the darkspawn got wind of it.
IMHO, if Loghain knew it was a suicide mission at Ostagar (as mentioned by the guy who got stabbed -- which starts the "return to Ostagar" mission) -- then Loghain could have easily defended his withdrawal position on that point ALONE. I would have supported Loghain 100% on his decision. However he did not have to declare the Wardens outlaws and poison the Arl. Doing that is ONLY to the advantage of the darkspawn.
Seems to me there is more going on than SUDDENLY he gets "personal ambition" -- considering his military background and previous battles with the darkspawn. If you study any history, you know the enemy must focus their target on the leadership. This leverage is fighting smarter instead of harder.