I feel like the best thing to do in regards to drug legalization is to try to empirically link each class/type of drug to various societal outputs, like productivity, price of medical care, etc, and then tax the drugs accordingly.
Meth decrease general productivity by 100%? Tax it at a higher rate. Cocaine/MDMA/LSD have benefits and fewer side affects? Tax them at lower rates.
Oh, how many times I've heard the same thing, except referring to opiates, cocaine, or amphetamines, rather than caffeine.