According to your rationale, oppressive regimes lead to increased drug abuse. Well, Spain also had a dictatorship for decades. The entire "Eastern Europe" lived under Soviet oppression for decades, too. The USSR didn't have a sexual revolution in the 1960s. I would love to see data that suggests that oppression causes people to go crazy and indulge themselves with drugs once they are "free". I am not saying it's not a possibility, but there's talk, and then there's data...
Almost all my friends in Portugal smoked Marijuana. They were not all that open about it, but everyone knew. By contrast, none of them ever touched cocaine or heroine. They were not stupid. Everyone had seen heroine junkies dragging themselves around town, their lives destroyed beyond repair.
Personally, I think the ones drawn to hard drugs are the weak people who can't deal with reality. Many of them die, but then... perhaps the purpose of their lives is to serve as warnings to others.