So I actually wanted to spin this off into it's own post bc while it is how I personally write my Tabris I have general thoughts abt this.
Tabris throughout the game is able to take (player-determined) revenge against several people that have directly harmed your community: Vaughn, Howe, and Calderius by killing all three. Alistair gets to not only see this, but then you deny him his revenge at the last possible moment?
But unlike those previous three, Loghain not only has more value alive than dead as a warden but also national hero with those still loyal to him, including his own daughter, this is such a parallel to Tabris themself.
Regardless of however you handle the origin, Tabris is labelled a criminal to be imprisoned and (very likely given canon) executed. Duncan "saves" you from that fate bc you are more valuable alive than dead, but it's not a kind fate and he tells you as much, even more so if Soris takes the blame, Duncan refuses to step in to conscript him too, as, whatever fate awaits him will be better than what fate awaits Tabris. Which he tells you in no uncertain terms.
Out of all of the origins, Tabris I think gets the full pragmatic warden experience directly in their face bc that's literally how they're forced to join.
So it's a rather tasty bookend to do the exact same thing to Loghain, and makes it all the more tragic for Alistair bc he can't see this is what Duncan would of done, and actually did through Tabris.