Grossman makes some eye-popping observations about the way that violent video games train kids to kill very similar to how the military trains recruits to kill, but without the stop button. He introduces evidence of the use of violent video games by young mass killers that the media/press mostly over-looked. He explains how the video game industry donates large amounts of money to politicians and scientists to keep this information secret or discredited.
He also describes just how violent, sexually explicit, and sexually exploitative (kill the prostitute instead of paying her, run her over with a car, spatter her blood all over) many of the popular games that kids are playing are - truly shocking. It's like psychopath training.
The rating system for video games is also not what most people think. There is is plenty of violence in games not rated M for mature. Killing human-like figures also can train you to kill humans. The games emphasize head shots and some use very brutal methods of killing humans or human-like figures with blood spattering.
He also discusses how much violence is a normal part of television and entertainment in general for kids and teens.
The first mass murder by a minor occurred in 1975. Compared to the tame television and entertainment of the 50s and early 60s, there was a huge increase in violent entertainment coincidental with the start of these underage mass killers. Since violent video games became a normal part of youth life, the number of mass killings by minors has escalated exponentially, and not just in the United States or where guns are legally available to adults.
China, for example, has had some horrible mass stabbings/killings of disabled people in homes. The violence is happening in many countries, even Japan, where violent crime has traditionally been very low.
Although we are told that our overall crime rates are down, Grossman points out that crime, violent crime, and bullying by teens is up, along with callousness.