For as many good things as we saw come out of the National School Walkout on Wednesday, we should have known that someone would do something to put a dark mark on the day. That someone was a custodian at Richland Northeast High School in South Carolina.

As I am writing this, thousands of school-age children are walking out of classrooms all across the country to protest U.S. politicians’ unwillingness to enact commonsense gun control. The nationwide demonstration is being hailed as a groundbreaking act of civil disobedience that seeks to protect the lives of…