GadolHadorah – If I understand correctly, your comments are referring to how the army should be run on the battlefield during a time of war. That is not what was I referring to. That is not the case most of the time, nor is it the case now, so that is not what anyone is talking about when they are describing how the army should be run.
Obviously, when someone is on the battlefield, they don’t run away because they hear a woman singing to herself in a foxhole (and if there are soldiers singing to themselves in foxholes, the Army definitely needs to be redone! 🙂
That is not where the kol isha issue came up in the army. The issue was that the Army was FORCING soldiers to attend PERFORMANCES of women singing publicly. That is completely assur, and there is no pikuach nefesh involved.
The Army clearly does not consider Israel to be in the same kind of emergency situation that you are envisioning if they have the time and energy to stage performances.
In any event, even in the emergency situation you are envisioning, the ONLY reason why it would be permissible for the soldier in question to not run away when the lady starts singing is because the halacha says not to, and NOT because we ignore halacha in such a situation. Halacha takes precedence over everything else, period! When we are mechalel Shabbos to save lives, it is only because (and when) the halacha says to do so.