It's bad to want to kill people.
John is a soldier serving overseas in a war time operation.
John wants to do his duty for his country.
John follows orders and deals with the reality of war while still understanding and respecting the consequences of his actions.
John begins to actively seek out firefights and danger on the battlefield.
John is able to eventually assimilate back into civilian life after years of counselling.
John gets lost in the darkest parts of war and never truly comes back from it.