In this case, I would add that the decision of taking such metric is a cultural one. The background of locals, their social structure provided Mills a better / wiser reference point in his overall strategy.
Indeed — glad that stood out for you. There is much in terms of cultural understanding that is required if we are to pick wise metrics.
To me, the question “Are two lives saved twice as good as one life saved?” is subjective and personal.
This article is making the point that if you agree with the axioms provided, there are certain conclusions that follow. The question itself cannot be rationally posed. You cannot measure the worth of any life, and cannot compare two lives with metrics. However, deciding to save one or two would depend, as you rightly point out, on personal and subjective factors — like “What can I do in this situation?”
Thank you for your great comments, Jean!