Japan had insane drug problems just after WW2. Not sure anything changed about their border since then?
You can even tax drugs quite a lot, and still keep the blackmarket small.
Taxation in California has proven to be a huge incentive to black market growers who can grow and sell tax free. The legal seller has the weight of taxation.
Your suggestions are basically a recipe for greater disaster.
What's different for those other drugs? Or should we (re-) criminalise alcohol and tobacco, too?
I agree that decriminalisation is a strange halfway measure. And I can also believe that not all policy in practice is great, even if the bears the label of 'legalisation' or 'decriminalisation'.
Japan was entirely controlled by the US after WW2 and had no control over its own affairs for several years. That's one big change. Plus culture changes a lot in a full century.
I know there are a lot of problems with meth, but how do they compare with other countries? (Per capita, say?)