ST. LOUIS — In the aftermath of Michael Brown’s death, legal activists suggested that some of the raw anger that erupted in suburban St. Louis had its roots in an unlikely place — traffic court. It was there, they said, that low-income drivers sometimes saw their lives upended by minor infractions that led to larger problems. If left unpaid, a $75 ticket for driving with expired tags could eventually bring an arrest warrant and even jail time. So courts began an experimental amnesty program …