Grossman's first book,
On Killing: The Psychological Cost of Learning to Kill in War and Society, is an analysis of the psychological processes involved with killing another human being. In it, he claims that most people have a
phobia-level response to violence, and that soldiers have to be specifically trained to kill. He details some of the physical effects that violent stresses produce on humans, ranging from
tunnel vision, changes in sonic perception, and
post-traumatic stress disorder. Robert Engen, in a paper for the
Canadian Military Journal critiquing
On Killing, criticized Grossman's works, saying that "although
On Killing and
On Combat form an excellent starting point, there are too many problems with their interpretation for them to be considered the final word on the subject." Grossman's response to Engen, printed in the same journal, attempted to address the criticisms by arguing that
S. L. A. Marshall's findings that man is not by nature a killer, even after having doubt cast on their methodology, have borne out in further scientific studies and real world experience, and furthermore, "have been the cornerstone of military and police training for over a half century." "On Killing" has been cited over 3300 times, noted by Google Scholar. In
Stop Teaching Our Kids to Kill: A Call to Action Against TV, Movie and Video Game Violence, Grossman argues that the techniques used by armies to train soldiers to kill are mirrored in certain types of
video games. He claims that playing violent video games, particularly
light-gun shooters of the
first-person shooter-variety (where the player holds a weapon-like game controller), train children in the use of weapons and, more importantly, harden them emotionally to the task of murder by simulating the killing of hundreds or thousands of opponents in a single typical video game. He has repeatedly used the term "murder simulator" to describe first-person shooter games. His third non-fiction book,
On Combat: The Psychology and Physiology of Deadly Conflict in War and in Peace, is an extension of his first, listing coping strategies for dealing with the physiological and psychological effects of violence for people who kill people in their line of work (soldiers and police officers). ==Criticism==