Only 20% of the total incarcerated population is in for a “drug offense.” Many of those are also very bad people. Almost all federal drug offenders are traffickers. Even if you don’t think that selling harmful substances to people is bad, there is the fact that many of these drug traffickers are involved in violent conduct. But the conviction often won’t reflect that conduct. Most violent and property crimes, unless performed on federal property, are state criminal law issues. Drug trafficking is usually the hook for federal law enforcement jurisdiction. The federal government doesn’t have jurisdiction to enforce state criminal laws. So someone may be incarcerated for a federal drug offense, even though there are state law violent and property crimes that could have been charged. (And states have little incentive to prosecute the state-law crimes for someone who is going to federal prison anyway.)
In order to get a more accurate picture, you have to not only look at the offense for which the prisoners are incarcerated, but also at prior criminal histories. (And even that will exclude situations where a first time drug offender is charged with a federal drug offense but there are also state violent and property offenses that could have been charged.)
https://www.brookings.edu/opinions/the-numbers-dont-lie-its-...
> For example, in a forthcoming Wisconsin Policy Research Institute (WPRI) study of the complete adult and juvenile criminal histories of prisoners from Milwaukee, WPRI analyst George Mitchell and I find that 91 percent of these urban criminals had one or more convictions for a violent crime. First-time drug offenders were less than 2 percent of the population. The imprisoned drug offenders had multiple arrests, bouts on probation, and adult and juvenile crimes, including auto theft, burglary, robbery, retail theft, domestic violence, sexual assault, drunk driving, jumping bail and, of course, drug dealing too.
> For example, in 1990, Harvard economist Anne Morrison Piehl and I studied a large sample of the Wisconsin prison population. We found that in the year before they were imprisoned, these prisoners committed a median of 12 crimes, excluding all drug crimes. In 1993 we studied a large sample of New Jersey prisoners and found exactly the same thing—they committed a median dozen crimes a year, again excluding all drug crimes. (Empirical studies by analysts at the National Bureau of Economic Research and elsewhere indicate that the average number of non-drug crimes that prisoners commit when free may be higher than twelve a year.)