The danger of becoming desensitized to violence is that we become numb to it. When we lose sensitivity, we lose the ability to feel the shock that violence evokes. We stop noticing the shock. We stop reacting with sympathy and empathy. In short, we stop caring. Obviously, this is a problem on many levels. On a personal, psychological level, one who is desensitized to violence will not be as averse to committing or preventing violence. On a social level, one who is desensitized to violence will be less likely to condemn violence on local, national, or international levels. Overall, a culture desensitized to violence will be more tolerant of violence and less inclined to prevent or stop violence when it might occur.
In "The Sniper," the main character is a young man, just past the age of innocence. This is important because it shows how war has changed him from an innocent young adult into someone capable of committing violence with little remorse:
His face was the face of a student, thin and ascetic, but his eyes had the cold gleam of the fanatic. They were deep and thoughtful, the eyes of a man who is used to looking at death.
The sniper is fighting for his life. He is in a war. So, he is killing in order to save his own life. But in addition to self-preservation, he has become machine-like in his ability to commit violence. He, once innocent, is now used to killing. That's why it is no problem for him to shoot the old woman who gives up his position. And this is why he is able to kill his "brother." The author underscores this idea of being desensitized when the sniper gets hit. There is no pain, just a "deadened sensation." It's as if he's even desensitized to violence committed against himself.
He does have a moment when he breaks out of this desensitization. After killing the enemy sniper, he feels remorse and curses the war and all it represents. But this moment of feeling and caring is fleeting. It is another act of violence (his revolver going off accidentally) that desensitizes him again, bringing him back to the state of being unaffected by violence. He is thus ready to be a killing machine again. The author ironically says that at this moment, the sniper is brought "back to his senses." It's as if to say "back to his senses" is to be back to normal. And in this case, "normal" means being used to killing.