JUDY WOODRUFF: But, first, we take a look at the latest wave of violence in Israel and the Palestinian territories, and how it connects to a new lawsuit against social media giant Facebook.

Chief foreign affairs correspondent Margaret Warner.

MARGARET WARNER: Last month on this Jerusalem bus, three Israeli Jews were killed by two young Palestinians wielding guns and knives, among them, 76-year-old Richard Lakin. The American-Israeli teacher, a longtime U.S. civil rights activist and educator, brought his family to Israel in 1984.

His son Micah Avni recounts the horror of his death.

MICAH AVNI, Son of Stabbing Victim: One of the terrorists, he shot my father in the head. My father fell to the ground. The other terrorist took out a knife and started stabbing him. He stabbed him multiple times in the head, in the face, slit his stomach wide open, cutting most of his vital organs.

MARGARET WARNER: Richard Lakin was among more than 70 targets of a new wave of attacks this fall on Jewish individuals by Palestinians. Since October 1, the Israeli Foreign Ministry says, at least 21 Israelis have been killed, and more than 184 wounded.

What's different, the vast majority of the attacks were by stabbing. Also notable, the assailants seem to be getting younger, as young as 12 or 13. Since the uptick in violence began, at least 86 Palestinians have been killed as well, shot during or after carrying out an attack, or in clashes with Israeli forces.

After Lakin was stabbed, his son struggled to understand.

MICAH AVNI: I asked myself, what would bring two 20-, 22-year-olds to board a bus and do something so brutal as to shoot three 70-year-olds and then to take a knife and start to cut them up?

MARGARET WARNER: Then, online, he discovered hundreds of Facebook, Twitter and YouTube postings encouraging Palestinians to stab Israeli Jews, and instructing them how to do it.

MICAH AVNI: Here's the instructional video showing how to most effectively slice somebody open with a knife in a way that my father was sliced open. They have a terrorist encouraging people to go out and stab Jews and showing how to best prepare a knife and sharpen it.

MARGARET WARNER: Avni believes such postings spurred the attacks on his father and others. He's now the lead plaintiff in a New York class-action lawsuit against Facebook. It was filed by the Tel Aviv-based Israel Law Center, which takes legal action on behalf of terror victims and against what it calls Israel's enemies; 20,000 Israelis have joined the suit.

First, it asks the court to order Facebook to stop allowing Palestinian terrorists to incite violent attacks against Israeli citizens. It also charges that Facebook's computers use algorithms to connect terrorists to users who've expressed interest in violent acts against Jews.

NOURA ERAKAT, George Mason University: It's not Facebook and YouTube and Twitter that is inspiring youth to take up knives against civilians. The root cause of this is the ongoing occupation and the violence, the military violence that's meted out against Palestinian bodies every day.

MARGARET WARNER: Noura Erakat is assistant professor at George Mason University outside Washington.

Are you saying you think these videos are insignificant?

NOURA ERAKAT: I think that they are insignificant relative to what Palestinians are actually producing.

MARGARET WARNER: And, she adds, there are plenty of hateful postings from the Israeli side too.

NOURA ERAKAT: Facebook was also the site of a page in the summer of 2014, that the page was, Israel demands revenge. Within less than a day, there were 37,000 likes on that page.

MARGARET WARNER: Facebook declined to grant us an on-camera interview, sending a statement that said in part: "There is no place for content encouraging violence, direct threats, terrorism or hate speech on Facebook. We urge people to use our reporting tools if they find content that they believe violates our standards, so we can investigate and take swift action."

The lawsuit, however, wants the court to order Facebook to remove content on its own.

Noura Erakat fears more vigorous policing by Facebook will be unfairly applied.

NOURA ERAKAT: What we can be assured is that Facebook will take a much more stringent approach to Palestinian speech in ways that they won't also apply to Israeli speech. So we will see the chilling of speech amongst Palestinians.

MARGARET WARNER: That prospect concerns First Amendment lawyer and national security expert Jonathan Turley of George Washington University.

JONATHAN TURLEY, George Washington University: Unfortunately, this is part of a trend that we have been watching occur in Europe largely, particularly France and England, where free speech is being eroded.

It's being eroded with the criminalization of speech that may be insulting or viewed as threatening to any group or individual. At the same time, we have seen civil litigation like this case where people are going to the courts to try to get injunctions. It's an effort to use the court to punish or chill speech.

MARGARET WARNER: Turley is just as critical of efforts to shut down Facebook's algorithms connecting violence-minded Palestinians with one another.

JONATHAN TURLEY: It's not just free speech that people want to limit. Once you limit free speech, they seek to limit free association. There's no question that — that companies like Facebook allow for dangerous associations to be made. The question is, are we comfortable with having the government or a court sit there and choose what are beneficial associations and what are not?

MARGARET WARNER: Most radical groups use social media for recruitment and propaganda. So says J.M. Berger, author of a book on ISIS and a scholar at the Brookings Institution.

J.M. BERGER, Co-Author, "ISIS: The State of Terror": What we're seeing is, there's a growing trend toward them using it.

WOLF BLITZER, CNN: Federal authorities arrested an Ohio man today, accusing him of spreading ISIS propaganda.

MARGARET WARNER: In the U.S., general incitement has rarely been prosecuted. But, lately, some people are being charged, he says.

J.M. BERGER: Well, the question of incitement to violence is a pretty complicated one. We had a recent case, an arrest of an ISIS supporter who had posted names and addresses of U.S. military personnel with an injunction to go kill those people. And that person was charged with incitement to violence, which we had not seen previously as a counterterrorism charge.

MARGARET WARNER: Global social media companies must walk a balancing act between protected speech and illegal content.

J.M. BERGER: Companies have to tailor their response to each country's rules and regulations. Turkey and Russia have been the source of a very large number of take-down requests to remove content, based on claims that the content is terrorist. But their definitions of terrorism are not necessarily the same as ours.

MARGARET WARNER: Turley believes the Paris attacks prove Europe's cracking down on violent content has been ineffective.

JONATHAN TURLEY: If you look at Germany, which has the longest experience on this in prohibiting even symbols like the swastika or people who deny the Holocaust, it hasn't made a bit of difference. The neo-Nazi movement has continued to grow.

By forcing these groups underground, you lose track, not only of them, but their views and how they're changing. Much of our actionable intelligence comes from being on these sites.

MARGARET WARNER: So your view is, on the Internet, just let 1,000 poisonous flowers bloom, whatever the effect?

JONATHAN TURLEY: No. You know, these companies have the right to pull material. There's a big difference between asking a government entity like a court to censor or strip speech.

MARGARET WARNER: In the U.S., policing of sites generally falls to the companies themselves, says Brookings' Berger:

J.M. BERGER: These companies suspend thousands of users every day for a variety of reasons, for instance, child pornography, other kinds of content and harassment. And what we don't have is any kind of disclosure of who they suspend and why.

MARGARET WARNER: One thing that can prompt them to act, he says, is negative publicity.

J.M. BERGER: The companies are extremely sensitive to bad press. Those stories will eventually have an effect, even on companies that claim to have a very high-minded mandate about free speech.

MARGARET WARNER: Facebook's response is expected in the New York State Supreme Court in January.

For Micah Anvi and his lawyers, even if their lawsuit fails, a publicity-driven change in Facebook policing policies would be a victory.

I'm Margaret Warner for the PBS NewsHour.