I disagree with your premise, but for the sake of argument let's just say it's true? By what sort of Naive thinking do you believe that wouldn't happen again? How are you gonna stop it if drugs are legal? You don't think the Columbians and the Afganis wouldn't ramp up production in an effort to "get another country hooked on a drug"?
Remember the Opium Wars was actually China trying to STOP the drug coming in.
In this case, the Drug dealers (the British) had more firepower than did the government of China. In an early effort to halt the flow of opium, one Chinese official burned a large shipment of the drug. (In Shanghai I believe.)
The British responded by bringing in warships and mercilessly shelled the town killing thousands. The Chinese begged for peace, and so the terms were dictated to them by the British, and those terms were the legalization of the Opium trade. People who want to talk about legalizing drugs should seriously study this period of history.
There's an important difference here — it isn't legalization only, but [essentially] the forced commerce as well.
I never said it wouldn’t happen again, in fact in my next post to you I outright say it could. Of course making them illegal doesn’t mean you stop them. Opium was illegal in part or in whole in China for your ENTIRE graph (medical use only as of 1729, banned completely 1799). Which hits the usual problem the WOD defenders never seem to be able to acknowledge: making something illegal doesn’t keep people from using it.
You’re right about one thing, people should study that period, and use it to understand that making something illegal doesn’t prevent use. You’ve got to work on your society to get people not to use drugs. Plenty of places had opium legal during that time frame and didn’t have the massive problem China did, and it was illegal in China. If you’re going to use this time frame as a “what to do” model the time frame says legalize, and nuke England.