On Thursday of last week, I represented the Marijuana Policy Project in a historic press conference in Los Angeles, joining fellow panelists Melissa Etheridge, Danny Glover, Hal Sparks, former New Mexico Governor Gary Johnson, and LEAP representative Steve Downing to endorse California’s Proposition 19, the measure to tax and regulate marijuana for adult use.  This was the first time world-renowned celebrities have spoken out in favor of Proposition 19, decrying the failed policy of prohibition. Melissa…