Why everyone seems to forget that the major problem is that the architect seems to already know the location of all the old gods.He can find them within 20-30 years, according to the wiki for the wardens is hard to reach the ancient dragons only because of the darkspawn and the locked streets.
But the architect can easly manipulate with his disciples 20-30 ogres and reach the other gods, unfortunatley it appears that no matter what, they cannot be killed without being corrupt.
So this guy is very dangerous, he can either protect the old gods
from being corrupted, or use them as a weapon to destroy the non awakened darkspawn, or the others races.
Even if he has good intention it's only a matter of time before a disciple try to kill him, look at the seeker the most dangerous disciple, he is still alive, he his the most clever and dangerous creature of all the series, with his trick he destroy both the humans and the elves.
SO in the end there is no real difference, we CANT KILL ALL OF HIS DISCIPLES especially the clever one the seeker, but if we elimintae the architect he cant create more disciples, but in the other hand no one take a look on the seeker.
anyway i choose to spare him, by considering the advantage and disadvantage
Advantages
1) Possibly end of the blights
2) Take a look on the seeker
3)Awake the darkspawn so they become more fragments instead of a unique army
4) Darkspawn are more resonable
5) With his researches he can find a vaccine against the taint
6) in the future he can stop other hostile darkspawn such as Corypheus, because he is still alive, and i think that corypheus can easly restore the research of the architect ad also he have a strong connection with the old gods and can easly find them to use them at his pleasure,and we know he is entirely evil.
Disadvantages
1) He fails and restore another mad broodmother with all the children (but hey probably he learns from his mistakes), ah and by the way you talk about the broodmother it seems that with the architect death you can stop the darkspawn by creating them, no impossible no one can stop the creation of other broodmothers
the only difference is that an awakened broodmother can be horrified by her new look,if she will be able to remeber what she was before
2)The new disciples can build an small army or a big one if they unite their efforts, and the non awakened darkspawn must follow their lead.
3) Grey wardens blood........
4) The taint is another problem, because if the new disciples,start
to want a better life and wish like morrigan to see mountains, the sea ecccc or simply want to use the taint as a weapon.... well we already know the disaster
Conclusion
It appears that only hurolock can become disciples i do not know why, but in the end i think that we have no choice because even if we choose to kill the architect, we cant stop the next generation of darkspawn, simply because his disciples are still alive, and corypheus is still alive, so in the end is better to give him a reason to trust humans, because i'm sure if he remember our kindness he will think twice-3-4-5-6 times before to start a new massacre, and probably most of the new disciples will follow the example of their messiah.