Tim O'Brien served in Vietnam. His collection of stories, "The Things They Carried," is a lightly fictionalized expansion of his earlier memoir about the war, "If I Die in a Combat Zone, Box Me Up and Ship Me Home."
Like many who fought in a war and lived to write about it, O'Brien conveys the sense of comaraderie and psychological torment inherent in the experience. His references to the vocabulary employed in day-to-day discourse of combat situations is meant to illuminate the manner in which men serving in a small unit like a squad or a platoon live a dichotomy. On the hand, they each recognize that they serve as one, each relying completely on the other for survival; on the other hand, they mask underlying sentiments like love and fear through the use of coarse, vulgar language. To display emotion is to appear weak and, consequently, a liability in the core mission of leaving the war zone alive.
To be considered "soft" is to be considered a danger to that core mission of survival. And, to appear to decry the taking of life in the context of war is unforgiveable. Human life, at least of the enemy, is cheap; to experience a vicarious thrill when sharing tales of killing enemy combatants is part of the psychological drill involved in maintaining one's proper role within the unit.
In today's military, similar psychological phenomena occur, even in peacetime. When a fighter pilot crashes his jet, dying in the process, the rest of the fighter pilot community decries the inadequacy of the deceased rather than question their own mortality. They prefer not to admit that the same thing could happen to them. They will not mess up.