(You didn't say the kinds of drugs, and maybe you believe that whatever he is selling is not bad, since you argue that marijuana is harmless and maybe he is selling only marijuana. But you did not say that and it is a pretty important caveat.)
While not condoning or agreeing with newt0311's argument, I wonder if whether the difference is a fundamental idsagreement with the place of individual human rights? Because newt0311 cites China and Singapore approvingly, I wonder if he believes that the harmony of society (or some other group-level values) are so important that the wishes and desires of individuals merit little consideration? In other words, drug addiction is so bad in its costs to society in general that the very lives of the individuals taking drugs are insignificant compared to the interests of society as a whole?
I only suggest this because if the disagreement is really at this level, arguing specifics and details will not be very fruitful.