Let’s be honest with ourselves: A censor lurks in all of us. When we encounter ideas and arguments that we believe are morally and factually wrong, we instinctively want them banned. When a speaker triggers our visceral disgust, we want him or her silenced, fired, ruined, and perhaps drawn and quartered. These impulses have been given free rein through most of human history, until that radical document, the Constitution, enshrined free speech as a fundamental right. But it’s a right that’s in constant conflict with our passions, and is thus always in danger—never more so than now. With the culture war at a boil, the clamoring for censorship has risen to a din. Books that discuss racism, homosexuality, and even the Holocaust are being banned from schools, and history lessons…