There is no scientific justification for rescheduling the marijuana plant when it is the amount of the psychoactive component (THC) in the finished product that should be determined and, based on that analysis, a decision on which schedule to place the individual product should be made.
A Schedule III classification requires evidence of moderate to low potential for physical and psychological dependence and abuse, but evidence already shows the potential for severe physical and psychological addiction and abuse from even casual marijuana use (especially with high potency THC products).