The problem is, that the same cultural stupidity that sees us pass new laws banning the newest designer drugs, is also the one that sees us banning relatively h

The problem is, that the same cultural stupidity that sees us pass new laws banning the newest designer drugs, is also the one that sees us banning relatively harmless and well-understood substances that have been used by humans for tens of thousands of years. And, I don't think it's possible to rhetorically separate the two in a way the public can digest. That is not to say you can't draw a logical distinction between the two that supports banning or strictly regulating the production and sale of one, while leaving the other alone - in fact I would say you've got a good start on doing that already. However, the distinction is subtle, and will be totally lost on a population that has had anti-drug propaganda shoved down its throat by the state for the last four or five generations. Any nuance in your argument will be seized on by drug warriors to justify banning the sale of e.g. marijuana or peyote, etc., and bring offenders into to the ever-growing all-consuming all-powerful prison complex.