Even ignoring that, let me ask you a question. At what point does something become "unnatural"? Where is this line you use to define these things?
I don't really like the terms "natural" and "unnatural". To an extent, everything can be classified as natural. Heroine and cocaine are "natural"--they both are derived from plants--but just because it is derived from something that was found in nature doesn't necessarily make it good or bad, as you've pointed out. I think the issue, in the case of drugs, comes when you start isolating alkaloids, and take the substance of it's "natural" context. It's the same idea with sugar and flour--both substances derived from plants: sugarcane and grain, respectively. Once you strip the fiber, and refine the sugar and starch, you are taking the nutrients out of their original form, and this is where you can start to get into trouble. The composition of whole foods is not just some sort of accident. The primary example is the fiber that is packaged with the sugars found in fruit: it is there for a reason, and it serves a distinct purpose in the digestion and metabolization of what you are consuming. Take the fiber away and just eat the sugar and you are, in my definition, eating something nature did not intend for you to, i.e., something "unnatural".