Before someone brings up "muh drugs" and only cites stats from federal prisons...
"In 2011, 55.6% of the 1,131,210 sentenced prisoners in state prisons were being held for violent crimes (this number excludes the 200,966 prisoners being held due to parole violations, of which 39.6% were re-incarcerated for a subsequent violent crime).[44] Also in 2011, 3.7% of the state prison population consisted of prisoners whose highest conviction was for drug possession (again excluding those incarcerated for parole violations of which 6.0% were re-incarcerated for a subsequent act of drug possession).[44]"