I bought this book hoping for an accurate look at the psychology of violence - however, it was literally saturated with specious points based on utterly fallacious arguments. The basic premises that Grossman makes are quite simply outright wrong; so wrong in fact that I am in the process of writing a thesis outlining how utterly naive his points are.
To list but a few:
1) Grossman claims that intra-species killing is not common in the animal kingdom, as it would not be evolutionarily selected for due to it being detrimental to the survival of the species. However, this is a complete misunderstanding of evolution; a process which doesn't care in the slightest about the wider species, and only favours organisms that better pass on their genes. Killing rival males (or the offspring of rival males) is an astonishingly common phenomenon throughout the animal kingdom. Indeed, it is the very reason we see such distinct sexual dimorphisms between males and females.
2) Grossman cites the work of S.L.A. Marshall, who allegedly conducted interviews of service troops in WW2 and beyond, determining that hardly any of the troops fired their weapons at the enemy. However, this work has LONG been discredited (since long before the publication of "On Killing"). Marshall fabricated his data almost entirely. He did conduct some interviews with a few service men, yet in follow up interviews none of the men recalled ever being asked how often they fired their weapons. Furthermore, Marshall published no methodology for how the interviews were conducted (meaning that it wouldn't even qualify as "qualitative research"), and certainly didn't include any statistical analyses (which would have provided a far more valuable "quantitative" measure)
3) Grossman cites "data" from the battle of Gettysburg, claiming that of the 23000 or so rifles that were recovered, many of them were loaded multiple times without being fired (these were all muzzle loaders). However, no independent historical data is available attesting to this anywhere. This is simply a fact that has wormed its way into the public consciousness, but doesn't have any basis. As far as I am aware (and so far I have researched fairly thoroughly) no systematic analysis was ever performed on the rifles recovered from gettysburg, and even if they were, that doesn't facilitate leaping to the conclusion that men weren't firing due to a crisis of humanity. There are many far more parsimonious explanations, such as misfirings that went unnoticed in the smoke, fear and confusion of battle.
4) Grossman blatantly ignores the real valuable data we have for many historical battles, that positively attest to the brutality of man kind. The fatalities of wars gone by were not produced by a select few psychopaths on the battlefield as Grossman suggests, but instead were caused by each and every man there. Humans ARE willing to kill, and the historical data demonstrates this compellingly and gruesomely!
5) Grossman asserts that we are living in a more dangerous society than ever, and infers that this is because we are surreptitiously and unconsciously exposing the minds of children to violence through the media in a similar way to the conditioning exercises used by the military to desensitize soldiers to combat. However, while the jury is still out on the media violence influence, a significant proportion of the data suggests that media violence does not have a significant effect on societal violence. Children are temporarily aroused by violence, but not permanently affected. Furthermore, the idea that society is more dangerous is itself a fallacy. We are in fact living in the safest time we have ever lived in, bar none. A multitude of sources provide evidence for this.
In closing, I would say that Grossman's take is a complete waste of time. It is based on incorrect premises from fallacious data sets, draws upon pop-culture psychology instead of the real science of psychology, and makes tenuous arguments throughout. I am amazed that it has been received as well as it is, and it saddens me that people accept him as an authority on violence, as it shows an utter credulity in his reading population.
Instead of bothering to read this waste of paper, I would instead recommend:
On the subject of prestate society violence: Lawrence Keeley - War Before Civilization
On the subject of human violence generally: Michael Ghiglieri - (THE DARK SIDE OF MAN) BY Ghiglieri, Michael P.(Author)Paperback Mar-2000
On the subject of wars throughout history: Matthew White - Atrocitology: Humanity's 100 Deadliest Achievements
On the subject of the decline of violence: Steven Pinker - The Better Angels of Our Nature: The Decline of Violence In History And Its Causes
On the subject of the denial of human nature: Steven Pinker - The Blank Slate: The Modern Denial of Human Nature (Penguin Press Science)
On Morality: Michael Shermer - The Science of Good and Evil: Why People Cheat, Gossip, Care, Share, and Follow the Golden Rule