"These results pose a challenge to those who wish to aggressively scale back incarceration, since the current politics of reducing sanctions for drug offenders is less complicated than that for reducing punishment for violent or property offenders."

I think there is an important difference between someone who is violent against other people versus someone who uses drugs (and might be violent in a sense to him/herself but no one else). So where "reducing sanctions for drug offenders" might be a novel thing to do, "reducing punishment for violent or property offenders" might not be. Apart from which one is "less complicated" or more efficient to the goal of scaling back incarceration.