I would have thought that power of drugs to create impulses in the form of addictions that lead to ex post facto rationalisations for the desire thereof would compromise the beneficient welfare aspects of the market that (putatively) derive from (putative) consumer sovereignty. It may be that the attempt to ban drugs has counterproductive results but I don't see how their legalisation squares with neoclassical economics either. This gets into that vast territory of consumer psychology about which I know nothing.
Yours, Rakesh