In a sad way, it's been very successful in the context it was enacted: as a tool to oppress "minorities". It was never about actual dangers from cannabis itself.
You're correct. John Erlichman, convicted Nixon aide, said as much:
"The Nixon campaign in 1968, and the Nixon White House after that, had two enemies: the antiwar left and black people. You understand what I’m saying? We knew we couldn’t make it illegal to be either against the war or black, but by getting the public to associate the hippies with marijuana and blacks with heroin, and then criminalizing both heavily, we could disrupt those communities. We could arrest their leaders, raid their homes, break up their meetings, and vilify them night after night on the evening news. Did we know we were lying about the drugs? Of course we did."
1994, talking to journalist Dan Baum, Legalize It All: How to win the war on drugs, Harper's Magazine, April 2016
Such revelation should cause heads to roll, people being released, pardoned and being paid compensation beside the end of prohibition. But there is not much happening. Why people are in such apathy?
"The Nixon campaign in 1968, and the Nixon White House after that, had two enemies: the antiwar left and black people. You understand what I’m saying? We knew we couldn’t make it illegal to be either against the war or black, but by getting the public to associate the hippies with marijuana and blacks with heroin, and then criminalizing both heavily, we could disrupt those communities. We could arrest their leaders, raid their homes, break up their meetings, and vilify them night after night on the evening news. Did we know we were lying about the drugs? Of course we did."
1994, talking to journalist Dan Baum, Legalize It All: How to win the war on drugs, Harper's Magazine, April 2016