I've heard this claim before and I think if it were true then the abuse of animals would not be so common place. The treatment of animals is, I think, largely cultural....hence why the vast majority of cultures protect some animals while abusing others.
So well-known there is no citation. I would be surprised if this was in fact true, humans like other primates are very good at compartmentalization.
But none of what you quoted answers my question, namely, why draw a line around the entire animal kingdom? The word "animals" in common language typically just refers to mammals and there is good reason to believe mammals, as class, are sentient.
Interesting that ypu ask for citations when you rarely if ever post any yourself. Here you are.
Animal Cruelty and Human Violence | Cathy Kangas
"According to the Humane Society of the United States, researchers determined that between 71 percent and 83 percent of women entering domestic violence shelters reported that their partners also abused or killed the family pet. 1 Another study found that in families under supervision for the physical abuse of their children, pet abuse was concurrent in 88 percent of the families. 2 In seven school shootings that took place across the country between 1997 and 2001, all boys involved had previously committed acts of animal cruelty. 3
Because of this growing evidence of a link between animal cruelty and violent crimes, those who abuse animals are now on the radar of law enforcement agencies, social workers, and veterinarians in states that have cross-reporting laws requiring these professionals to report cases of animal abuse."
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http://www.nytimes.com/2010/06/13/magazine/13dogfighting-t.html?pagewanted=all
"The connection between animal abuse and other criminal behaviors was recognized, of course, long before the evolution of the social sciences and institutions with which we now address such behaviors. In his famous series of 1751 engravings, “The Four Stages of Cruelty,” William Hogarth traced the life path of the fictional Tom Nero: Stage 1 depicts Tom as a boy, torturing a dog; Stage 4 shows Tom’s body, fresh from the gallows where he was hanged for murder, being dissected in an anatomical theater. And animal cruelty has long been recognized as a signature pathology of the most serious violent offenders. As a boy, Jeffrey Dahmer impaled the heads of cats and dogs on sticks; Theodore Bundy, implicated in the murders of some three dozen people, told of watching his grandfather torture animals; David Berkowitz, the “Son of Sam,” poisoned his mother’s parakeet.
But the intuitions that informed the narrative arc of Tom Nero are now being borne out by empirical research. A paper published in a psychiatry journal in 2004, “A Study of Firesetting and Animal Cruelty in Children: Family Influences and Adolescent Outcomes,” found that over a 10-year period, 6-to-12-year-old children who were described as being cruel to animals were more than twice as likely as other children in the study to be reported to juvenile authorities for a violent offense. In an October 2005 paper published in Journal of Community Health, a team of researchers conducting a study over seven years in 11 metropolitan areas determined that pet abuse was one of five factors that predicted who would begin other abusive behaviors. In a 1995 study, nearly a third of pet-owning victims of domestic abuse, meanwhile, reported that one or more of their children had killed or harmed a pet"
