Capitalism has a deep-seated taboo against taking recreational drugs. So strong is the taboo they will ruin your life and exile you from mainstream society for doing something recreational.
This is changing a bit as the scientists tell them there is basically no reason for this. But the scientists meet with resistance from entrenched cops, judges, lawyers, who are very 
about it.
What's the materialist explanation for this moralistic taboo?
Glad to see the Atwater interview mentioned, that's largely how I view the purpose of the war on drugs. They can't make it illegal to be black or poor, the war on drugs is the loophole for that.
Not to mention, I'm sure there's some influence from the legal drug industry (alcohol/liquor and pharma) at play.