1) Why is the spirit that you save from the taint an abomination? Kieran isn't turned into a monster. On the contrary. He's a perfectly normal child who hosts a purified bit of soul inside him, which is then taken from him by Flemeth later on.
-It's an abomination because it match the technical definition of the meaning.
A magical being is inside a body that do not belong to it and is influencing and altering the behaviour of the host which make the OGB an abomination.
When it is removed the child is even more screwed up than before.
2) The assumption that every Warden does the DR for selfish reasons is wrong. Some Wardens do it because consider Morrigan and Flemeth to know more about the old magic surrounding the taint, the Archdemon and the darkspawn better than the Wardens, with their stark philosophy and their hermetic magical rituals whose origins are now forgotten in the sands of time.
Other Wardens do it because they want to help preserve whatever spiritual creature is contained within those Old Gods. They are ancient and powerful magical creatures. That's what Dragon Age is about: magic and wondrous things. Shouldn't something like that be rescued from the darkness and preserved?
And other Wardens do the DR because they do not wish to see Alistair die. If you don't sacrifice yourself,he does. And they don't want that. Either because they love Alistair or wish for him to become king in order to balance Anora's political ambitions.
The assumption that every Warden does the DR for selfish reasons is right until proven otherwise.
-Given that they never explained their rationale nor they ever told anything to the warden making an assumption about what they do know or what they don't know is just a guess.
-Tyrannical dragons worshipped by slavers and co-founder of an empire of slaves rumoured to be responsible for the blights and potential archdemons?
Great wonders indeed!Those wardens who agree to the DR under the premises of saving something " pure" don't even know what they are doing.
-If the warden is gambling the world for Alistair/Loghain that's indeed ipso facto selfishness incarnate.
So on what moral grounds will they judge and condemn the HoF for aiding an actual mage that DOES know WHAT an Old God is, WHAT kind of magic is involved in its creation and how to best tackle the problem of dealing with the Archdemon, with the bonus of avoiding the senseless waste of lives, something the Wardens have horribly failed at for centuries?
Based on what premises you are saying that Morrigan know what an old god is when it was proved the contrary?
The senior warden is the one which is tasked to kill the archdemon.
-Corin senior warden die by killing Zazikale he was going to die for the calling anyway.
-Loris senior warden die killing Toth he was going to die for the calling anyway.
-Gharael senior warden die killing Andhoral he was going to die for the calling anyway.
-Loghain he deserved that death anyway
Not being used by the witches of the wilds doesn't count as failure and being spared at the cost of gambling the world and empowering Mythal and the Dread Wolf isn't a success either.