But there was also another reason.
"In addition, there has been much discussion in the Senate regarding combatting radical Islam. Notably, Islam is currently the fastest-growing religion among prisoners in the United States. Sending people - often young people - who may already come from broken homes and difficult family situations into a brutal prison environment is potentially a breeding ground for radicalization," Paul wrote.
Paul's stance got a quick response from the Kentucky Democratic Party.
"Rand Paul says that he is helping to keep drugs on Kentucky's streets because he wants to make sure criminals aren't converting to Islam - you simply cannot make nonsense like this up," chairman Dan Logsdon said in a statement. "If he's so worried about prisoners converting to Islam that he is willing to place the lives of Kentucky's children at risk by allowing dangerous drugs on our streets, my advice to Senator Paul is that he just go ahead and make crime legal so we won't have prisons any more. Rand Paul needs to regain whatever toehold he had on reality and realize that what he is doing is going to hurt Kentucky's children in a very real way and he is going to have to live with that."