When Elon Musk bought Twitter a year ago, he said he wanted to create what he called a “common digital town square.” “That said,” he wrote, “Twitter obviously cannot become a free-for-all hellscape.” A year later, according to study after study, Mr. Musk’s platform has become exactly that. The Consequences of Elon Musk’s Ownership of X Now rebranded as X, the site has experienced a surge in racist, antisemitic and other hateful speech. Under Mr. Musk’s watch, millions of people have been exposed to misinformation about climate change. Foreign governments and operatives — from Russia to China to Hamas —...