A unique conglomeration of events in American history seemed to converge in the early 1950s to spur on a the Confederate flag fad. The 100th anniversary of the Civil War was just around the corner, the differences between the South and the North became more overt as segregation began to be changed in de facto and de jure ways in the early 50s (see the Jackie Robinson story of the late 40s, as well as the birth of the Civil Rights movement around that time) and white Southerners began to resist the beginning of the end of overt and socially acceptable white priviledge, and lastly rebellious teen culture just began to creep towards the mainstream from society's fringes. There's a Master's thesis in there somewhere, but I'll just leave it there.
The point is: fads seem to come out of nowhere, but they have a social cause and ignition point. These causes and igniters tell us about our society.