For all the distance of his time and place,” Greil Marcus wrote in Mystery Train: Images of America in Rock ’n’ Roll Music, Robert Johnson “draws a natural response from many who outwardly could not be more different from him.” In 1975, Marcus must have been thinking of Cream (“Crossroads”), the Rolling Stones (“Love in Vain”), and Led Zeppelin (“Traveling Riverside Blues”), among other blues-fancying Brits. In 2008, the humor website Stuff White People Like attacked its target demographic for affecting to appreciate “Black Music That Black People Don’t Listen to Anymore.” Where Greil Marcus saw performers and audiences transported by something dark and elemental in country blues, today’s cynics see only theft and posturing.

It is a testament to the power of the blues that people are so proprietary about it, so...