Indeed, if you value a soldier's life the same as a human's life, you really don't want them on the battlefield any more than absolutely necessary to defend against the invaders.

Spears and catapults and bows make your soldiers effective dozens of yards away from the enemy.

Rifles get your soldiers to a hundred, sometimes two hundred yards away.

Artillery and drones make your soldiers effective up to a few miles away.

The further away you can keep your soldiers while accomplishing your goals, the better.