Recent research and scholarship suggests that ordinary humans have the capacity to carry out mass violence and that this capacity can be conditioned. Whitworth University professor James Waller, author of Becoming Evil : How Ordinary People Commit Genocide and Mass Killing has been one of the leaders in investigating the factors which seem to precede episodes of mass violence. Waller argues that the capacity for mass violence is a normal one and that it can be conditioned, or brought out, by various environmental factors including societal polarization and also the use of demonizing and dehumanizing language, and other forms of hate speech

( from the Whitworth news release on Waller's book ) "Waller's Becoming Evil refutes many of the standard explanations for antisocial behavior and presents four ingredients that lead ordinary people to commit acts of extraordinary evil. Waller contends that being aware of our own capacity for inhumane cruelty, and knowing how to cultivate the moral sensibilities that curb that capacity, are the best safeguards we can have against future genocide and mass killing.

"To offer a psychological explanation for the atrocities committed by perpetrators is not to forgive, justify or condone their behavior," Waller states in his preface. "Instead, the explanation simply allows us to understand the conditions under which many of us could be transformed into killing machines. When we understand the ordinariness of extraordinary evil, we will be less surprised by evil, less likely to be unwitting contributors to evil, and perhaps better equipped to forestall evil."

James Waller's research is far from singular - his work is buttressed by other recent, striking research into the process by which humans can be conditioned to carry out acts of mass political violence.

New Scientist, Nov. 24, 2004 ) "All humans are capable of committing torture and other "acts of great evil". That is the unhappy conclusion drawn from an analysis of psychological studies.  Over 25,000 psychological studies involving eight million participants support this finding, say Susan Fiske and colleagues at Princeton University in New Jersey, US.  The researchers considered the circumstances surrounding how individuals committed seemingly inexplicable acts of abuse in the midst of the US military's torture of Iraqi inmates at the Abu Ghraib prison in 2003 and 2004. "Could any average 18-year-old have tortured these prisoners? I would have to answer: `Yes, just about anyone could have.'", Fiske says.

"In the years up to 1994, many journalists allied themselves with Hutu extremists who planned and carried out the genocide. A magazine called Kangura, or Wake Him Up!, published screeds denigrating Tutsis as a subhuman race that aimed to destroy Rwanda, and urged Hutus to arm themselves. As the genocide got underway on April 6, 1994, the radio station RTLM filled the airwaves with vitriol, even broadcasting the names of individual Tutsis and their hiding places. Confirming the media's murderous role, the UN war crimes tribunal for Rwanda in December convicted key figures from the magazine and the radio station of incitement to genocide."

"Considering the enormity of the task, it is tempting to play with theories of collective madness, mob mania, a fever of hatred erupted into a mass crime of passion, and to imagine the blind orgy of the mob, with each member killing one or two people. But at Nyarubuye, and at thousands of other sites in this tiny country, on the same days of a few months in 1994, hundreds of thousands of Hutus had worked as killers in regular shifts... What sustained them, beyond the frenzy of the first attack, through the plain physical exhaustion and mess of it?" - from We Wish To Inform You That Tomorrow We Will Be Killed With Our Families: Stories From Rwanda, by Philip Gourevitch

James Waller's 2001 groundbreaking work, "Becoming Evil : How Ordinary People Commit Genocide and Mass Killing",  was based in part on extensive interviews with both the victims and perpetrators of mass political violence, from many of the notable outbreaks that have marred the 20th Century :  The Holocaust, the Rwandan Genocide, the "Killing Fields" of Cambodia, the mass killings by government death squads in Central American during the 1980's, and other such incidents.

In an August 22, 2002 interview for Salon by Suzy Hansen, James Waller describes what he calls "the ordinary nature of extraordinary evil", and

Hansen: "We always hear about the dehumanization of victims, but how does it actually work and what's the process behind it?"

Waller: "It allows us to more easily commit the evil that we want to commit because we're not committing it upon someone who's a moral equal or a fellow human. You see it in wartime: military groups and countries describe the enemy in certain terms -- like Vietnam, with "gooks." We do what we need to strip our enemy, our victims, of their humanity. In many ways for us it's a psychological defense mechanism because if we see their faces, if we know they're human, if we know they have a husband, wife, children, mother, father, those things make it more difficult to kill.

In the book, I refer to Franz Stangl, a commandant at Treblinka, who was asked after the war was over: When all the inmates came to Treblinka, you knew you were going to kill them in 24 hours, so why all the humiliation? Why the beating? Why did they have to run around naked? Why did you spit on them and call them names? Stangl's response was incredible. He said that they did that because it made it easier for their men to do what they had to do."

Hansen: "The us-them mentality seems to work here too. It's unsettling that studies have found that that doesn't necessarily have anything to do with a preexisting prejudice."

Waller: "Most people don't understand how easy it is to develop us-them [mindsets]. Experiments have been done where people come in and a coin is flipped to decide if they're going to be in group A or group B. The groups have no interaction whatsoever, but you ask the groups to evaluate each other on attractiveness, intelligence, warmth, honesty and so on. People in the groups, even though they don't know the people in their group or the other group, tend to just favor their own group. They see their group as more attractive, healthier, less likely to be institutionalized at some point.

Us-them thinking doesn't require a lot to become operative. Any simple way we want to divide ourselves as us-them will develop a pattern of thinking that favors my group and disfavors the outgroup. That can start off very innocuous but pretty quickly can become dangerous."

A paper released by Waller - Perpetrators of Genocide: An Explanatory Model of Extraordinary Human Evil ( link to 18 page PDF file of Waller's paper ) - preceding the publication of his book provides a shorter version of  Waller's evolving theory of the psychology of mass violence :

( note : as summarized here, on Metafilter.com )The first ingredient is universal human nature, with its three dangerous tendencies to xenophobia, ethnocentrism, and aggression in pursuit of power. The second ingredient is the personality of the ordinary person who commits the atrocities and how much it's been influenced by three things: cultural ideology or propaganda; willingness to exclude the victim from the protection under a moral code; and ego investment in an organization supporting the atrocities. The third ingredient is defining the victims as the "other." And the fourth is the power of three situational factors to influence thoughts, feelings and behaviors: the escalating process of brutalization in which perpetrators learn to kill (a gradual desensitization or habituation to atrocities); the binding factors of the group that shape our responses to authority (peer pressure and conformity, male ritual and camaraderie, diffusion of responsibility and a distinctive culture of cruelty); and the power differentials that exist between perpetrators and victims.

Waller is far from alone in his thinking :

See, for example, Moral Disengagement In The Perpetration Of Inhumanities, by Albert Bandura ( pdf file ) :

"Rapid radical shifts in destructive behavior through moral justification are most strikingly revealed in military conduct (Kelman, 1973; Skeykill, 1928). The conversion of socialized people into dedicated fighters is achieved not by altering their personality structures, aggressive drives or moral standards. Rather, it is accomplished by cognitively redefining the morality of killing so that it can be done free from self-censure. Through moral justification of violent means, people see themselves as fighting ruthless oppressors, protecting their cherished values, preserving world peace, saving humanity from subjugation or honoring their country's commitments. Just war tenets were devised to specify when the use of violent force is morally justified. However, given people's dexterous facility for justifying violent means all kinds of inhumanities get clothed in moral wrappings."

In 1996, Gregory H. Stanton, writing at the U.S Dept. of State, authored a work - later presented  at the Yale University Center for International and Area Studies in 1998 - entitled Eight Stages of Genocide. Writes Stanton :

Genocide is a process that develops in eight stages that are predictable but not inexorable. At each stage, preventive measures can stop it. The later stages must be preceded by the earlier stages, though earlier stages continue to operate throughout the process. The

eight stages of genocide

are: Classification, Symbolization, Dehumanization, Organization, Polarization, Preparation, Extermination, and Denial

For further reading, see the following sources:

One of the best writers on the subject of hate speech - especially hate speech from the American right - is without a doubt Dave Neiwert, who writes Orcinus and does extensive coverage on this. For an extremely extensive database of Christian and religious right hate speech, see HateCrime.org.