That's just it RR, you're making my point for me.
Yes, if he goes against the rules he agreed to follow then he would be solely responsible for his actions, as an individual.
But what if the army sanctioned his actions? What if they expected it from him, and encouraged it? What then? Would the army still not be responsible for the consequences of such?
You see, many atrocities, were commited in the name of Christianity, and were sanctioned by the Church.
And, one cannot use the excuse that the Church is not Christianity, because, in a sense, it is.
For it is the Church who primarily brings Christianity to the people, and shapes their view of it.
Christianity is not some abstract entity. Christianity is the people that it is composed of. For without the people, there would be no Christianity.
"The good Christian should beware the mathematician and all those who make empty prophecies. The danger already exists that the mathematicians have made a covenant with the devil to darken the spirit and to confine man in the bonds of hell." - St. Augustine