Call it old as you may but some truths are timeless whether you want to admit to their wisdom or not.
A conscience that lives contentedly knowing it is helping the enemy is about as valuable as the conscience of any Nazi who ever lived who tried to hide behind his consciencious attention to "duty."
Such an appeal to one's conscience is not only meaningless, it is often harmful. An observer might fairly wonder what sort of "conscience" such a person has to begin with.