And yet, on a platform like YouTube, there are reasons to be skeptical about the potential of what experts call “counterspeech.” Libby Hemphill, a computer-science professor at the University of Michigan’s Center for Social Media Responsibility, studies how different kinds of conversations, from politics to TV criticism, unfold across social media; she also prototypes A.I. tools for rooting out toxic content. “If we frame hate speech or toxicity as a free-speech issue, then the answer is often counterspeech,” she explained. (A misleading video about race and science might be “countered” by the video made by AsapScience.) But, to be effective, counterspeech must be heard. “Recommendation engines don’t just surface content that they think we’ll want to engage with-they also actively hide content that is not what we have actively sought,” Hemphill said. “Our incidental exposure to stuff that we don’t know that we should see is really low.”