Why do people commit hate crimes -- violent, cruel and pointless offenses motivated by a baseless abhorrence or disgust for a group of people they perceive as different from themselves?

NYC officials recently announced that hate crimes have increased by 35 percent this year. Mayor Bill de Blasio put the blame on our new president-elect, Donald Trump, who ran a campaign villainizing immigrants and urging that the names of Muslim people entering the United States go into a registry.

Experts say de Blasio, who asked Trump to become “a force of reconciliation,” is correct in correlating the uptick to Trump’s rhetoric, and echoed his request that Trump forcefully declare that bias crimes are unacceptable.

Hate crimes typically surge whenever a dominant group perceives itself under threat: There was a 1,600 percent jump in hate crimes against Muslims in the six months following 9/11, noted Jack Levin, co-director of the Brudnick Center on Violence at Northeastern University. Similarly, gay bashing rose nationwide after Massachusetts became the first state to legalize same-sex marriage in 2004.

Episodic increases tend to settle back down over time, but the current spike and its cause, “is something we’ve never seen before. It’s something new. All these people on the margins now hear this speech in the mainstream and can express their violence with moral impunity,” Levin said.

Another difference?

Historically, the majority of hate crimes in the United States were committed by young men in groups, who beat up a scapegoated “other” for thrills, a feeling of power and superiority while cementing group bonds. But since 9/11, there has been a precipitous increase of adults -- mostly men -- engaging individually in hateful acts against innocent victims, many of whom are Muslim, Levin said.

Nationally, “only four percent of all hate crimes are committed by members of white supremacist groups,” Levin noted. But easy internet access to the hatred they espouse has validated and emboldened many others to act out hostilities.

The Friday following Election Day, Edward Dunbar, a clinical professor of psychology at UCLA, received a call from a publisher asking him to write a book about the election and the rise of hate crimes. “The nationalism and xenophobia is a political cataclysm,” Dunbar said. “Outgroups are now being targeted because they lost,” in the passionate contest for America’s identity, he said.

Many offenders are simply violent people with a high levels of aggression and antisocial behavior who are likely to have grown up in violent homes, and often with a history of having been abused themselves, said Dunbar, who is on the verge of publishing a three-volume history titled “Hate Crimes as Domestic Terrorism.”

At least half of all perpetrators “have a prior history of other non-bias-motivated offenses,” Dunbar said. The commission of a hate crime is often “a signifier of a worsening of their criminal lifestyle,” he said.

Hate crimes are not crimes of passion, but of premeditation, continued Dunbar, who notes that offenders will often travel to harm a random stranger. “The majority of hate crimes have nothing to do with financial gain. They’ll beat up the lesbian and leave her wallet or purse,” Dunbar said.

Some people with mental illnesses may not have the ability to analyze and parse hate speech for what it is, said Naftali Garcia Berrill, the executive director of New York Forensic in Brooklyn. “The political climate and the zeitgeist affect the mentally ill: If someone is paranoid and all they hear about is terrorists and Muslims,” they can be triggered to commit a hate crime, Berrill said. “People remain tribal, and under stressful conditions they regress,” to primitive behaviors, he added.

Which puts the United States in a tough spot. “We have a First Amendment that prohibits punishing hate speech,” which prevents interceding before hate speech escalates into hate-based behaviors, Levin said. “Using racial slurs and epithets is simply not against the law.”

And what should be done with those who commit hate crimes?

That’s tricky, say experts, as one of the most hate-filled places in the nation is prison. “Hate crime offenders are embraced by the racialized groups in prison, then they become more racialized and more violent,” as Dunbar explained.

Levin doesn’t believe first-time offenders should be jailed, but be given stringent probation with tailored community service. He told of a white teenager in Boston who had thrown rocks through the windows of homes where people of Cambodian descent lived. The offender was sentenced to do work in the Cambodian community and emerged from his sentence “genuinely remorseful. It really worked!” Levin said.

But is it fair to expect members of target groups to educate and change the distorted beliefs of perpetrators?

Perhaps the most helpful interventions are prevention-based. Levin wants more structured opportunities in schools for children of diverse backgrounds to “come together in the spirit of cooperation to achieve goals they all share.” Superficial encounters with the “other” don’t do much to excise prejudice, Levin said. “There has to be interdependence.”

“You have to create critical thinking in people, so they can think things through,” when tempted to behave antisocially, Dunbar said. Dunbar is also in favor of early interventions, but said it is also imperative that leaders set a tone of tolerance and the need for everyone to be treated respectfully. And there needs to be continued support at the federal level for “hate crime enforcement,” which he fears may not be present in the coming years.

Berrill had his own prescription: “Cognitive therapy, education and a clear, unambiguous message from the people in authority that certain behaviors will not be tolerated.”