Welcoming the freshman class in August, Cornell University President Martha E. Pollack admonished students: “Free speech, as difficult and as challenging as it is, is not only the bedrock of higher education. It’s also the bedrock of democracy and a free society.” But when conservative author Anne Coulter appeared at an event there earlier this month, a group of hecklers shouted, clapped, and whistled until Ms. Coulter, herself a Cornell alumna, had to leave the stage.