Do tech companies need to rethink online content moderation?
No - the question of liability
Private companies cannot be responsible for the actions of a very few extremists. In the United States, Section 230 of the Communications Decency Act removes liability from social network providers, as they are not the “content provider” of the extremist and/or illegal content. Social networking services may have to remove content that that is sensitive or illegal, in a similar way to copyrighted contents, and many things have been done to counter and remove extreme content quicker. But the prevalence of terrorism remains a problem of the society affected not the problem of social media platform used to spread such content, users are simply using new media broadcasting tools, tech companies are therefore not liable for this huge issue, it's a societal problem and requires a societal response.