When the Controlled Substances Act was passed, it included many, many drugs that had been previously criminalized under several different and conflicting laws. That act was an attempt unify drug policy. Nothing can be inferred from that act about why any given drug was or was not criminalized. However the timing of the act is a bit curious, given it happened shortly after a rise in drug use in a class of people who were anti-authoritarian and talked a lot about the cultural effects of drugs.
For your links, here are 2: the first espouses the premise -