As tensions continue to mount in cities across this country, sometimes with alarming and devastating consequences, we increasingly hear calls from responsible leaders to “lower the temperature.” To tone down the rhetoric. To step back from the brink. These calls are not meant to challenge the sanctity of free speech. Freedom of expression remains among the most cherished rights in our society and a cornerstone of American democracy. Rather, they reflect a growing recognition that provocative and vitriolic language can sometimes be as destructive as knives or bullets. Words, when used recklessly, can inflame passions, dehumanize neighbors and set entire...