Ethan Nadelmann, the founder and executive director of the Drug Policy Alliance, doesn't think kids and teens are going to start using marijuana more frequently if the drug is fully legalized across the country. The reason is simple: They can already get pot pretty easily.

"There are three national surveys in which young people say it's now easier to buy marijuana today that it is to buy alcohol. In every high school in America, marijuana use is now more or less omnipresent. In the surveys for the last thirty years, 80 percent of young people say it's easy to get marijuana. So I don't think that's the group where it's going to go up. If anything, you're going to take away some of that forbidden fruit attraction to marijuana," he said during a panel discussion at the Aspen Ideas Festival last week.

So who will start using more marijuana if it's fully legalized? Nadelmann, a legalization advocate whose organization was founded to stop the "war on drugs," points to the grandparents of the world. "It's going to be people in their 40s, 50s, 60s, 70s, 80s, and 90s," he said. "It's going to be older people going, 'Damn, it helps with that arthritis, I didn't realize that.' Or, 'It helps me sleep at night,' or 'I actually find I prefer it to having a drink at the end of the night, or 'You know what, I prefer it to the pharmaceuticals my doctor is giving me for my mood or my anxiety.'"