Facebook said it struggled to identify the video of the New Zealand mosque shootings because of the use of a head-mounted camera by the gunman, which made it harder for its systems to automatically detect the nature of the video.
It is intermediary's responsibility that they should control the contend in their platform. But in this situation, it is hard to detect whether they are harmful. The algorithm behind focusing on popularity, but they can also add the harm of the content into consideration.