Your highlighting does not make anything more clear. The fact is that I communicated a hypothesis, based on the facts that I know, and some assumptions about the intellect and observation powers of our ancestors.
Based on the fact that you believe that spelling out some of the facts and assumptions that go into formulating a hypothesis is "backpedalling," I must assume that you know very little of the scientific process, which is based on the process of hypothesis formulation.
But here, let me spell it out for you:
1) The history of marijuana delegalization as promulgated by groups like NORML is highly suspect. The fact that it consists chiefly of conspiracies makes any part of it unreliable. Hence, I do not (and perhaps cannot) know the real reasoning behind the laws making it illegal.
2) The effects of marijuana use were not studied when it was uniformly illegal; most researchers did not think that getting the DEA licenses to conduct research on marijuana was worth the time and effort. However, since many states have decided to "legalize" marijuana, the urgency of such research has become paramount. Hence, researchers are now studying every aspect of marijuana use, and what they are finding and publishing is that marijuana use is quite deleterious.
3) Our ancestors were not stupid. They would have been able to see the effects of long-term drug abuse (marijuana, opium, whatever), even if they did not have the extensive medical documentation that we are now collecting.
Hence, my hypothesis is a logical assumption based on the facts listed above that our ancestors made marijuana use illegal because of its harmful effects.
By saying "I'm certain"? Is that the language with which hypotheses are typically communicated in your circles?
Our ancestors were snickered on hard cider.