My interpretation is that they trying to make the point that it's not just the "War on Drugs" that is causing this massive spike in prison population but is instead being driven by increasing penalties across the board, including increasing the number serving life, stated or otherwise, without possibility of parole.
They make this point while acknowledging that the "War on Drugs" does disproportionately affect African Americans and women.
Throughout the article they make several statements that indicate to me they think there should be more discretion allowed on deciding which punitive actions should be taken.