Via the Dish, Russ Belville makes a list. The first reason:
It might seem counter-intuitive to some, but illegal marijuana is much easier to acquire than regulated marijuana because weed dealers don’t check ID’s. Four out of five high school seniors, more than three in five sophomores, and two in five middle schoolers (8th grade) say marijuana is “fairly easy” or “very easy” to get. One third of 16-17-year-olds say marijuana is easiest to buy, not cigarettes, alcohol, or prescription drugs. Two out of five teens say they can get marijuana in a day; almost one in four can get marijuana in an hour. Obviously letting unregulated dealers control the marijuana market is not protecting your kids from access to marijuana. On the other hand, aggressive enforcement of ID carding for minors, combined with public education have led to some of the lowest rates of teen alcohol and tobacco use ever recorded.