This was so not unforeseeable.
“Cannabis is potentially a real public-health problem,” said Mark A. R. Kleiman, a professor of public policy at New York University. “It wasn’t obvious to me 25 years ago, when 9 percent of self-reported cannabis users over the last month reported daily or near-daily use. I always was prepared to say, ‘No, it’s not a very abusable drug. Nine percent of anybody will do something stupid.’ But that number is now [something like] 40 percent.”
The Atlantic, America's Invisible Pot Addicts