Why is America so slow to exonerate the wrongly convicted?

While the wheels of justice turn slowly, the old aphorism goes, they grind exceedingly fine. Yet, as the civil rights activist Rev. Benjamin Chavis told me almost 50 years ago, “they rarely operate in reverse.”

Back then, I covered Chavis’s post-conviction hearing for the New York Times. Chavis led the Wilmington Ten, whose criminal case became a political cause. Their 1971 arrest for arson and conspiracy followed urban unrest in the North Carolina port city. Armed white vigilantes and...