Here's the common knowledge people have:
A Warden has always battled the Archdemon. A Warden has always killed the Archdemon. A Warden has always died fighting the Archdemon. An Archdemon is a giant dragon. Giant Dragons can seriously maim, maul, mutilate, and mangle a person, if not outright mash them into mush.
Considering people don't know jack **** about their intricate secrets that they will kill over and even Riordan says outside eyes shouldn't see (I have to headcanon just how Anora found out, as I talked about earlier, but also where Genitivi learned it boggles my mind) it's not unreasonable to understand where Loghain was coming from, because people operate under the belief that all a Warden happens to be is a group of people who fight Darkspawn and Darkspawn only.
Which is true, but there's more to it then that that those common folk do not understand because they just don't know.
If I'm hearing tales of how Wardens ended the Blights all the time and I know they went up against a giant Dragon.... and they died.... I'm not going to assume there's some magical element at play here. I'm going to assume the Wardens died in the battle from injuries sustained.
As far as a non-Warden would be concerned, Garahel would've died from having his body thrown clear across Ayesleigh, not from some magic hocus pocus element.
EDIT: And hell, it's not like Loghain didn't want the Warden taken alive. He makes it clear to the men in Lothering they were to bring in any surviving Wardens alive, while Cauthrien was told to bring the Wardens in -- admittedly her instructions were dead or alive, but she does offer you the chance to surrender. If you're taken prisoner, your wounds are treated and you're still kicking in Fort Drakon.
Not the best place to be, all things considered, but we have no idea what Loghain was hoping to do. More then likely, try us for killing Howe -- much as he deserved that death, our methods of doing it should realistically be seen less as self-defense (since only we can say that's what it was) and more as murdering a man in his home considering Wardens can't just kill nobles indiscriminately without fear of reprisal, as Duncan states and the Dryden Rebellion illustrated.
Still, I like to think that Loghain would at least meet with the Warden and/or Alistair to talk about the order, perhaps give them "one last chance to show they will fight for Ferelden", as he might state.