He wrote the book as a homage to the common infantryman. It's in his dedication. It's also I think him asking questions. Asking the reader to think about what the price of survival is. At what point do you lose your humanity? How do keep it and survive as a species? When you ask your youngest to fight for you and become maimed in body and soul, do they not deserve that "privilege"? He also advocated in the book that the officers fought with their men and never left them behind. Heinlein had many questions and thoughts in all of his books and left the thinking to you.