Racists, misogynists, anti-LGBTQ goons, and disinformation merchants have plagued the social media site for years. Trolls with two followers regularly provoke fights with more popular users just to garner the capricious attention of a subtweet. Nasty posts aimed at celebrities are so abundant, Jimmy Kimmel has a recurring segment “ Mean Tweets ” on his late-night show with celebrities reading aloud the insults of their anonymous haters. It’s not that Twitter has ever been perfect. Far from it. Twitter can be a mess. But it’s been our mess, like an unruly friend who brings enough joy and insight that it’s...