As Facebook pushes into developing countries, it tends to be initially received as a force for good.In Sri Lanka, it keeps families in touch even as many work abroad. It provides for unprecedented open expression and access to information. Government officials say it was essential for the democratic transition that swept them into office in 2015.But where institutions are weak or undeveloped, Facebook’s newsfeed can inadvertently amplify dangerous tendencies. Designed to maximize user time on site, it promotes whatever wins the most attention. Posts that tap into negative, primal emotions like anger or fear, studies have found, produce the highest engagement, and so proliferate