Extremism experts say hate must be stopped at community level before it's too late Calls to address online hate speech after Buffalo mass shooting New details shed light on how the gunman in the Buffalo mass shooting was exposed to racist conspiracy theories online and the social media platforms he used to plan the attack, prompting calls for more oversight to prevent further tragedies. Whether it goes by the "great replacement" or another name, the conspiracy theory embraced by the accused Buffalo, N.Y., gunman has inspired several mass shootings in recent years — in Canada and around the world. Ten...