Grannyknot I agree with you, nothing is simple, the costs of alcohol addiction both on a personal and societal level are horrendous, but prohibition in America just didn't work. Legal highs frighten me, at least with the more usual illegal substances hospitals knew what they were dealing with.
However, I do believe that some drugs which are illegal at the moment have great potential medically, especially cannabis and the psychedelics.
Kew Gardens has been running a series of weekends called the Intoxication Season, I heard from someone who works at Kew that the one on Cannabis was very good.
You mentioned LSD, yes it was harmful if taken in the wrong circumstances, and I wouldn't want it to be freely available on the street (although of course it is!) but it did lead to great creativity and other benefits, (two Nobel Prize winners said that it had helped their discoveries) banning it put an end to all research.
The first trial in 40 years has just been published, there is a very good video talking about it on Huff Post Live.
HuffPost Live interviews MAPS Founder Rick Doblin, PhD, David Nichols, PhD, and John Halpern, MD, about the recently published results from MAPS’ study of LSD-assisted psychotherapy to treat anxiety associated with advanced-stage illness. The experts speak about the variety of conditions that can potentially benefit from psychedelic-assisted therapy and share their perspectives on the past, present, and future of research in this area.