I've heard counter-facts (from some black leaders in the U.S.) that the prisons aren't filled with primarily non-violent drug offenders, largely because release programs don't keep them for very long given the bursting-at-the-seams prison population and they're the first to be let out.
So the notion that U.S. prisons are simply filled with non-violent drug offenders could well be an unfounded wives' tale that people keep repeating as if it's fact.
Regardless, there's a misinformation war in place which basically clouds a lot of any useful discussion about race, poverty, and incarceration in America.