During the 2012 CMT Music Awards, Willie Nelson, a country music legend and well-known marijuana supporter, performed his song, “Roll Me up,” a marijuana ballad whose refrain is “roll me up and smoke me when I die,” a clear allusion to marijuana. Joining Mr. Nelson in singing verses of the popular song were some of country music's best and brightest: Darius Rucker, Toby Keith, Zac Brown, and Jamey Johnson. It is refreshing to see mainstream musicians that are thought to cater to a relatively conservative…