Im thinking the statement of it being a plant from the earth is directed more to why its illegal as opposed to the whole "being all natural" thing. I've heard people refer to the first page in the bible where it states how god put plants and herbs for us.... go figure... A "plant" better yet a "weed" that is, if found in your possesion illegal.
Not saying I agree/disagree with it. Just clearing up your OP.