I don't think Facebook could win that one. If they purged all instances of it they would be accused of concealing evidence of the genocide after the message got out - which it certainly would have. Like Syrian attrocity footage being taken down for policy violations. If they shut down during the time period they would be guilty of concealing and stopping pleas for help. Large scale moderation is a mug's game that ends only in being Kafkatrapped when it gets remotely political.