Look, here's my take on it. This would make things so much easier to enforce/regulate.
If a substance grows naturally, or is the product of natural processes, and is then consumed by eating, smoking, brewing into tea, or otherwise consumed in this natural state, then it should be legal. This should include food, wine, beer, pot, opium, mushrooms, coca leaves, banana peels, bacon, and pure cane sugar (sugar, not other white granular substances). The American people should be able to buy and use these without gov't intervention as long as they do not directly endanger anyone else by their resulting behavior.
The people should be able to grow their own 'herbs', make their own beer and wine, for their own consumption without gov't regulation.
Production, transport, storage of these items for profitable sale should be regualted much like food is today. You may need to meet certain codes for safe handling, storage, and packaging, but that's it. Substances that are created by physical distillation of the aforementioned substances, like hard liquor, may have some regulation, like hard liquor does today.
Substances that are artificially synthesized, chemically created or modified, or otherwise man-made should be controlled like pharmaceuticals. By prescription only, with FDA regulation, efficacy and safety testing.
There. Nobody needs Crack if they can go out to their garden, or take a walk down to the local smoke outlet, and smoke a little weed.