What Role Do Social Media Platforms Play In Radicalizing People?

Funerals have begun for the 50 people killed last week in the attack on a pair of mosques in Christchurch, New Zealand. Six victims were laid to rest today.

We're learning more about how the alleged gunman sought to spread a hateful message. In the days before the shooting, he posted links to a racist manifesto across social media in more than 60 places, according to the Washington Post. He also live-streamed the attack on Facebook, and the video continued to appear elsewhere on social media in the ensuing hours.

Facebook reports that the live footage was viewed fewer than 200 times, but the company also says it went on to remove roughly 1 and a half million uploaded copies of the video in the next 24 hours.

Over on YouTube, Google engineers worked through the night to identify and take down hundreds of thousands re-posts of the video.

So what responsibility should companies like Facebook, Google-owned YouTube, Reddit, and Twitter have for this kind content? And what role do these platforms play in radicalizing people like the shooter, in the first place?

Joan Donovan, who directs the technology and social change research project at Harvard Kennedy School's Shorenstein Center on Media, Politics and Public Policy. She tweets @bostonjoan.