“Your homework,” the writer, teacher and peace activist Colman McCarthy used to tell his students, “is to tell someone you love them today. And if you can’t find someone to tell that you love them, look a little harder. And if you still can’t find them, call me up. I know where all the unloved people are—they’re everywhere.” McCarthy, who died on Feb. 27 at the age of 87, had a well-deserved reput...