Yep, it's a legit quote, just abbreviated. He was asked about his view in an interview prior to the release of DKR. You can read it here here
You’ve also been a big proponent of the legalization of marijuana.
Marijuana! Heavens, oh yeah. It’s just the stupidest law possible, given history. You don’t stop people from doing what they want to do, so forget about making it unlawful. You’re just making criminals out of people who aren’t engaged in criminal activity. And we’re spending zillions of dollars trying to fight a war we can’t win! We could make zillions, just legalize it and tax it like we do liquor. It’s stupid.
You can read about a lot of important figures' views on marijuana on that site - http://marijuanamajority.com