I have yet to meet anyone (present company excluded?) that is an advocate of marijuana use that will concede that simple truth: that even moderate use of marijuana can cause tremendous harm.Do you count everyone who opposes criminalization of marijuanna as "an advocate of marijuanna use"? Because there's another possibility. The one that describes me in fact: I don't personally use marijuanna, nor do I want my children to, but I believe that choice should be left up to individual adults to make for themselves. Note the carefully chosen words: choice, adults.
As for your assertion of the "simple truth: that even moderate use of marijuana can cause tremendous harm." If you are simply referring to a case where someone was driving while impaired, the same could be said of countless people using cell phones or eating while driving. Do you propose criminalization of food and cell phones? Even while not driving?