The whole point of drinking darkspawn blood during the Joining to become a Warden, is that you'll be able to slay the Archdemon during a Blight. Otherwise the Archdemon will be resurrected by possessing the nearest Darkspawn, if the Archdemon is slain by a Warden, the Warden gets possessed instead, and they both die.
Which means the Wardens are stuck with the taint, until it starts corrupting them from the inside, that's when the Calling comes into play, a Warden that hears the Calling, must then go to the Deep Roads and kill as many Darkspawn as he can, until he is killed by them.
If the Warden doesn't do anything at all, he'll succumb to the taint and become a Ghoul.
When all the Wardens started hearing Corypheus' bluff Calling, they became terrified, they thought that they will all die from the taint leaving Thedas defenseless against the Sixth and Seventh Blight, and sought to kill Razikale and Lusacan with a demon army, before the Darkspawn would turn them into Archdemons.
Of course, the purpose of that bluff was to get the Wardens raise an army of demons for Corypheus.