I love the 'Howe was the one who did it' arguments for the sheer volley of stupidity being dredged up. First of all, the scene where Zevran is hired, (which btw the PLAYER NOT THE WARDEN sees) Howe is merely the messenger, coming in with Zevran. It's Loghain who gives the order, it's Loghain Zevran says hires him (later when you interrogate him) and it's Loghain who would be paying the bill for said assassination (which I don't imagine was cheap, also prompting more slavery crackdown by Loghain). It's Loghain, not Howe, who wastes resources fighting with his fellow nobles instead of just admitting he was wrong to usurp Anora's throne and stepping down. Pretty sure the more loyal nobles who were just opposing him (versus those who were grabbing for what land/power they could in the chaos) would have gotten behind Anora and helped. In fact, in that conversation Howe advises him to stop fighting with his fellow countrymen and start going after the darkspawn but the "greatest general in Ferelden" (read:Idiot) insists he can do it all by himself. Caladrius mentions Loghain BY NAME when he's trying to bargain with the warden, saying he knows you because you are all Loghain talks about. Loghain's was the name signed on the dispensation papers letting them come in to take men, women and children into slavery (to blood mages). Regardless of second class citizen status, elves were citizens of Ferelden too, Loghain just picked them because he thought no one would care. Mentioning it won't give as many points as talking about Eamon's poisoning, but none of the nobles thought selling elves into slavery was a 'good idea'.
I hate Loghain, and that hasn't faded at all in the years since I first started playing this game. He's an idiot, a traitor, and a slaver and I don't see any sign of repentance or regret at the conversation with him in Denerim with Eamon and at the Landsmeet (the only time the warden can truly see and confront him in game). Without metagaming or some creative roleplaying (which I can see happening), Loghain's crimes deserve death (or at least life imprisonment). The game however pigeon-holes you into killing or sparing him.
The level of stupid of Riordan cannot be expressed either. Seriously, in ALL of Ferelden ONLY Loghain is available for the Joining? WTF is the point of the 'rite of conscription' if it allows you to recruit only ONE person in all that time, a person who, up to now has been trying to kill you.
And killing Loghain isn't 'murder'. It's a rightful execution. The Landsmeet is a TRIAL for his crimes. The PC is on trial (since Loghain is trying to prove you are in cahoots with Orlais for killing the king). One of you must win, the other will be executed for his crimes. The free for all that ensues is Loghain trying to stage a coup if he loses, Eamon doing the same if the PC loses. The duel called for is "trial by combat" in which might makes right and the victor is claimed the winner of the Landsmeet. Once you trounce Loghain (or if you are beaten and it's game over) the loser expects to be executed for his/her crimes. That's how it goes. Even Anora expresses regret it came to that point, but she doesn't hold it against the PC for what was done.
So, off with his head every time in my games and aside from doing right in front of Anora, I have no qualms with it.