Amnesty International, Human Rights Watch, and the United Nations can all talk about "the Geneva Convention." But that agreement on the rules of war has never applied to combatants not wearing the uniform of any country that is a party to the Geneva Convention.
Terrorists wear no uniform and show no mercy, as they have repeatedly demonstrated by beheading innocent civilians, including women.
Why any such terrorists should be captured alive in the first place is a real question. Maybe they have information that could be useful. But every terrorist our troops try to capture alive increases the risk of death for American combat troops.
Their information better be damned important for that.
Mister Terrorist could have stayed home and lived a human life, but instead he chose to exist as an animal and prey upon the innocent and the helpless.
We don't need to make the effort to mentally dehumanize our enemy when he has already chosen to dehumanize himself.