A Natural Instrument

Because everyone has one, the voice is often called the most natural instrument there is.

Because everyone has a voice, it is often described as a natural instrument. But I think this characterization obscures the long hours of training that must go into the production of a beautiful tone, especially in the case of classical singing. Quite frankly, there are some voices out there we'd rather not listen to. What do you think? Is the voice natural or as cultivated as the rest?