Yeah but it's not patentable. There are many drugs that have the potential to cure all sorts of diseases that never make it to market for this reason.
"I'm just not sure why you would not take the next step and isolate the active ingredients and synthesize them so that people can benefit from something with predicable dosages and a price affected by economies of scale."
Because often they work less well and have more dangerous side effects. There literally is no isolated molecule that on average will produce better results than the whole plant, even though what you're getting from the plant is a little different each time.
The first rule of recreational drug use is rotate your receptors. E.g. if you keep hammering the exact same receptor with the exact same molecule each time, bad things are going to happen. The same thing often applies to medicinal drugs, in which case standardization tends to be worse on average than taking a random cocktail of chemicals, even if you don't know what it is your taking. Again, c.f. the research on marijuana vs pure THC for a good example of this.
"What I still don't understand is why you think that some beneficial compound that's adulterated and present in unpredictable amounts in plant form is better than the alternative?"
Because that's what the evidence says is often the case. It doesn't really make any logical sense, it's just what happens to be true. A good example of this is the TED video Eating To Starve Cancer, where they talk about how mixing a bunch of different types of tea together is more anti-angiogenic than any individual tea:
Even if you were to standardize some mixture, there is no reason to believe that taking the same mixture day after day would be more effective than taking a different mixture each time.
Also, you can actually standardize plant medicine now. Plants are cloneable, and you can grow them in highly controlled conditions and then blend them together the same way they blend tea or champagne. (Which is why champagne from a good house tastes almost exactly the same despite the wildly different growing conditions each year. Same for things like Lipton english breakfast tea or whatever.)
"I sympathize with your bias towards the naturalistic fallacy"
The naturalistic fallacy is assuming that if something comes from nature it must be better. That's not at all what I'm saying here.