The subject here is combat. It involves killing. Killing is only justified if it is done to protect Life, rights and Freedom, otherwise, barring accidents, it is always evil... even if, "The man has a combat assignment and he follows orders." That man may be ignorant, but that's not relevant in determining whether the killing was justified, or not.
A sniper is no different than a line infantryman or a bomber pilot. All have assignments in combat and follow orders. In the case of a sniper his assignment is to kill individuals - specific individuals. Somehow people perceive that role as different than anonymous killing by dropping bombs. It's not.
You attached the "ignorant" word to this. How is that relevant? What is this soldier ignorant of? He does his job, follows his orders. That's what soldiers do.