A Palestinian mother encourages her child to kill Jews.

Several women’s advocates recently put the spotlight on misogynistic postings to Facebook promoting and celebrating violent attacks on women. As a result of their pressure on advertisers and others, Facebook eventually responded — admitting it could do better in policing online hate and outlining a series of steps that it planned to take to address hate speech.

That episode reflected a slice of a problem we have worked on for years — an epidemic of online hate that is harming individuals and society. Today, the virus of Internet hate is metastasizing every day in ways that Hitler and his propagandists never could have imagined.

This scourge of online bigotry and its consequences are the subject of our new book, “Viral Hate,” which proffers an overview of the problem and looks to Internet providers, governments and society at large for creative new solutions.

Our book does not make the case for stifling free speech, nor is it an attempt to cast aspersions on the Internet itself for the problem. In fact, we celebrate and defend this wonderful tool for information-sharing, research and social networking, and conclude that one solution to the problem of online hate may be more speech, not less.

Some simply shrug off online hate as the inevitable effluent of Internet freedom and rationalize it as a problem too big to address. After all, every second on the Internet, there are more than 700 posts to Facebook, and 600 Twitter tweets. Every 72 hours of video are posted to YouTube.

Much of this content is harmless, and yet a disturbing amount of online content is anti-Semitic, racist, homophobic and misogynistic. It can overwhelm sites in seconds. Recently, YouTube was flooded with racist comments after an otherwise harmless cereal advertisement featuring a bi-racial child, her white mom and black dad went viral. The video site was forced to shut down the comments section until they had found way to stop the flood of racist invective from poisoning the discussion.

Hate has indeed gone viral.

Online hate traumatizes its targets. It also serves to rally and attract others who might share its bigoted message.

Hateful ideas have led some people to take action offline, in the real world. There have been widely reported attacks minorities and suicides that started with Internet hate speech or online bullying.

What is more, while the Internet is a terrific tool for gathering research, there are many instances where young children have turned to the Internet for a homework assignment and found themselves confronted with false “historical information,” such as racist sites purporting to tell the “true story” of Dr. Martin Luther King Jr. or Holocaust denial sites masquerading as purveyors of truth.

Also disturbing is that many people react to the common appearance of online hate by treating it as the norm, and ignoring it.

The problem of scale — the sheer volume of Internet content — is no excuse for not trying to deal with online hate. When viruses causing disease spread, society responds even when the scale of the problem is daunting. Likewise, the virus of hate requires a broad response.

Internet hosts like Facebook and Google have joined with the Inter-Parliamentary Coalition for Combating Anti-Semitism and the Anti-Defamation League in a working group that includes civil rights experts for an ongoing collaboration on ways to reduce hate speech. Terms of Service and their enforcement, tools for counter-speech as an antidote for hate speech, and education are the current focus.

All the while, the right to free expression always is in mind. And yet, more is greatly needed from the Internet community, especially the companies that knowingly or unknowingly play host to hateful content.

For starters, the companies need to learn why some content it is hosting — like Holocaust denial — is indeed hate speech, as are jokes using anti-gay epithets. And they need to put adequate resources in place to respond to complaints about the presence of hate-filled posts, and to take down those posts promptly.

And more is needed from parents and educators. Teaching kids about cyber-literacy and online civility is a start, and we do a woefully bad job of that in this country.

And as demonstrated by the women pushing Facebook to change, people who use the Internet need to speak up when they see online hate. “When you see something, say something” should not be restricted to unattended parcels. We each have a duty to speak out against online hate.

Edmund Burke’s pre-Internet warning still applies: “The only thing necessary for the triumph of evil is for good men to do nothing.”

Abraham H. Foxman is National Director of the Anti-Defamation League. Christopher Wolf, an attorney who specializes in Internet privacy law, is the League’s Civil Rights Chair. They are the co-authors of “Viral Hate: Containing Its Spread on the Internet (Palgrave Macmillan, June 2013). This article was originally published by Fox News.