Why will many a man have the courage to die gallantly while will not have the courage to think that the cause for which he is asked to die is an unworthy one?

Answer 1

Any soldier in combat would totally deny that "die gallantly" part. Plain trembling, shaking frightened out of their wits and puking up their breakfast is a better way of describing it. That is human nature.

The purpose of the Army is to train men and women to forget their personal selves and work as an unbreakable team. The result of this is, that in combat, most soldiers would rather die than run away and let their buddies die. That, and soldiers who run away from combat are usually shot dead or court-marshalled and hanged.

No true combat soldier needs to or has time to think about "the cause" - and it's near 100% sure that average soldiers don't know what the cause even is. An army where soldiers think about the "cause" is a horribly trained army, and all its soldiers will likely die in combat rather than defeat the enemy.