This is not a question of Feynriel's life versus others' lives.
This is Feynriel's life versus the POSSIBLE harm to others (including death) if Feynriel can't resist, he should be killed or Tranquiled(?) (whichever he prefers, or if he refuses to decide, killed)
Unconscionable is the perfect word, it is wrong, end of statement, to kill somebody because of something they have no control over. It's also sometimes necessary. I would want him to see that, because ultimatley this is his life, and neither Marethari nor his mother have the right to decide whether or not he should die. I may have the obligation, because sometimes you must act for the greater good and Coventry needed to be bombed.
Mmm but you see IT IS, a question of the half blood's life versus other lives, he if he survives as a mage he goes to the Imperium.
How many slaves, blood thralls and servants do you think he is worth? How many do you think he'd kill before he even completed his apprenticeship?
Far Reaching consequence and all that, but as i said before.
When you said between order and chaos, oblivion and life, you don't get the privilege of a "soul". It's a luxury that you cannot afford, Morality is ultimately selfish, and for some one who stands against the bulwark and protects the masses, you cannot have it.
So i'd ask again how lives is that boy worth?
Lets hear your answer.