Also, I take issue with this meme that 25% of all those incarcerated are locked up ONLY for non-violent drug charges. For that to be true, it would require that ON AVERAGE one in for convicts behind bars was guilty of either using or selling drugs, without any associated crimes, like robbery, assault, possession of a gun, etc., and that is simply unbelievable.
There is a lot of evidence for statistics like this, you can start with http://en.wikipedia.org/wiki/War_on_Drugs#United_States_domestic_policy.
Federal prisons were estimated to hold 179,204 sentenced inmates in 2007. Of these, 15,647 were incarcerated for violent offenses, including 2,915 for homicide, 8,966 for robbery, and 3,939 for other violent crimes. In addition, 10,345 inmates were serving time for property crimes, including 504 for burglary, 7,834 for fraud, and 2,006 for other property offenses. A total of 95,446 were incarcerated for drug offenses. Also, 56,237 were incarcerated for public-order offenses, including 19,528 for immigration offenses and 24,435 for weapons offenses.
According to a federal survey of jail inmates, of the total 440,670 jail inmates in the US in 2002, 112,447 (25.5%) were drug offenders: 48,823 (11.1%) for possession and 56,574 (12.8%) for trafficking.