I think it was pretty decent how they allowed a "warrior" to join their world. It happens in many films, books and stories where one person, the most unlikely person is chosen for a greater purpose.
Were we watching the same film? Not everyone in the army was portrayed as cold hearted; the woman left
! I'm guessing you, or someone close to you is in the Army, that's why something like that "upset" you. It's not something new for a room full of armed forces talking to be cheering at the idea of killing and defeating an enemy.
To be honest, I'm pretty shocked you thought there was no variety to the world. The variety and imagination expressed in the film was one of the things I liked about the movie... Maybe it's because I, myself have no imagination, but gosh, I'm still surprised, lol.