Just to be clear -- heroin is processed morphine, which comes from poppy sap. Cocaine is processed coca leaves. Nicotine is primarily extracted from tobacco leaves. Belladonna, strychnine and digitalis... just because something is made from a plant doesn't make it less of a drug or less dangerous.
The most dangerous drugs aren't really comparable, though. They tend to be processed concentrates of the plant, and in those cases the plant itself is much less harmful than the concentrate.
Consuming plant matter directly with minimal processing is quite a different thing from isolating the active ingredients as much as possible, creating dosages much higher than found in nature and simultaneously removing buffering material such as fiber and other nutrients.
