What explains such unspeakable evil? What sort of human being deliberately butchers a sleeping baby, or plunges a knife into a toddler’s heart?

As news of the massacre in Itamar spread, candy and pastries were handed out in Gaza in celebration. The Al-Qassam Brigades, a branch of Hamas, argued that the murder of Israeli settlers was permitted by international law. A day later it changed its tune, insisted that “harming children is not part of Hamas’s policy,” and suggested instead that the massacre might have been committed by Jews. The Palestinian “foreign minister,’’ Riyad al-Malki, also voiced doubt that the killers could have been Palestinian. “The slaughter of people like this by Palestinians,’’ he claimed, “is unprecedented.’’ Actually, the precedents abound.

The atrocity in Itamar recalls the 2002 terror attack at Kibbutz Metzer that left five victims dead, including a mother and her two young boys. It brings to mind the murder of Tali Hatuel and her four daughters, who were shot at point-blank range as they drove from Gaza to Ashkelon in 2004. It is reminiscent of the bloodbath three years ago in a Jerusalem yeshiva, where eight young students were gunned down. Unprecedented? If only.

The civilized mind struggles to make sense of such savagery.

There are those who believe passionately that all human beings are inherently good and rational creatures, essentially the same once you get beyond surface disagreements. Such people cannot accept the reality of a culture that extols death over life, that inculcates a vitriolic hatred of Jews, that induces children to idolize terrorists. Since they would never murder a family in its sleep without being driven to it by some overpowering horror, they imagine that nobody would. This is the mindset that sees a massacre of Jews and concludes that Jews must in some way have provoked it. It’s the mindset behind the narrative that continually blames Israel for the enmity of its neighbors and makes it Israel’s responsibility to end their violence.

The truth is simpler, and bleaker. Human goodness is not hard-wired. It takes sustained effort and healthy values to produce good people; in the absence of those values, cruelty and intolerance are far more likely to flourish.

For years the Palestinian Authority has demonized Israelis and Jews as enemies to be destroyed, vermin to be loathed, and infidels to be terrorized. Children who grow up under Palestinian rule are inundated on all sides — in school, in the mosques, on radio and TV, even in summer camps and popular music — with messages that glorify bloodshed, promote hatred, and lionize “martyrdom.’’

None of this is news. The toxic incitement that pervades Palestinian culture has been massively documented. What children are taught in Palestinian classrooms, Hillary Clinton said in 2007, is “to see martyrdom and armed struggle and the murder of innocent people as ideals to strive for. . . . This propaganda is dangerous.’’

An estimated 20,000 mourners accompanied the Fogel family as they were laid to rest in Jerusalem Sunday. In his eulogy, Vice Premier Moshe Ya’alon predicted bitterly that in time the Palestinian Authority would honor the Fogel family’s murderers and name public squares after them. His comment might have seemed gratuitous — except that at that very moment, in the West Bank town of Al-Bireh, Dalal Mughrabi was being celebrated at a public square named in her honor. It was Mughrabi who, 33 years earlier, led a PLO terror squad on a savage rampage on Israel’s Coastal Road. Thirty-eight innocent Jews died that day, 13 of them children. Boston Globe