This can be stated more simply. Being a sniper is the soldiers' assignment. It has nothing to do with the forces of evil. The man has a combat assignment and he follows orders. Apparently he is good at his job. Well done!
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.