Of course we need to be able to value lives and trade them off against other resources; we do it all the time when we make policy or safety decisions.

I think the issue of lives in the context of "sums" is this: how many lives did "we" lose, compared to how many lives did "they" lose, in order to come to a conclusion of the conflict in and of itself. The sum is only self-referential....what happens afterwords is not relevant to the argument.

e.g. in a $10 zero sum experiment, the "winner" leaves with $9 and goes and buys crack on the street. The "loser" takes his/her $1 and buys a winning lottery ticket.

The long-term winning and losing after a war is not quantifiable, because there are no controls. Too many decisions, laws, random chance, weather events, could have taken things in one direction or another...who's to say?