When researchers at a non-profit that studies social media wanted to understand the connection between YouTube videos and gun violence, they set up accounts on the platform that mimicked the behaviour of typical boys living in the U.S. They simulated two nine-year-olds who both liked video games, especially first-person shooter games. The accounts were identical, except that one clicked on the videos recommended by YouTube, and the other ignored the platform’s suggestions. The account that clicked on YouTube’s suggestions was soon flooded with graphic videos about school shootings, tactical gun training videos and how-to instructions on making firearms fully automatic....