My,my. Some people have a remarkably short memory.
The Warden mages were controlled by blood magic, as Livius Erimond demonstrated to the Inquisitor in the Tevinter ritual tower.
Hands up; hand down.
And anyone who disagreed with Clarel was expelled or threatened by their colleagues, just like Loghain was. And why?
Because all the Wardens thought they were ABOUT TO DIE.
The false Calling, emitted by the Nightmare demon, remember? It's like feeling excrutiating pain everyday because all of a sudden, you have terminal cancer. You don't think rationally, you just DO whatever you have to do before you die.
So it was either to follow her lead and build a demon army with the purpose of killing the last 2 Old Gods or every Warden thought he/she would be dead in a matter of days, with no one to stop a future Blight.
I would offer that both of you raise good point. Most of the Wardens were not controlled, but they were heavily influenced. However, even if the calling had been real, it would not have been the end of the Wardens. Recall that in the first book alluded to in DAO Duncan was brought in from another country. So even if all the Wardens in Orlais and Ferelden died, more would have come from elsewhere. The order would not have been destroyed.
Now as I follow this discussion, Wardens exist to stop the blight, not to fight darkspawn. Everyone fights darkspawn, but according to Warden lore only Wardens can kill archdemons. They established this order to prevent the blight from destroying humanity. Fair enough. What I am not understanding is how summoning a demon army that will also destroy humanity is better than the darkspawn destroying it. Moreover, Clarel was not the first to summon a demon army. That honor goes to Sophia Dryden as far as I know. Of course it does prevent blights, but it is far beyond foolish thinking. It is foolish and highly dangerous thinking. It serves the point that while the Wardens might bbe peerless warriors, they aqre not sound strategists as far as we have seen. That they would seriously consider it let alone act upon it shows how their zealous fanaticism needs to be checked with a capital C.