There ARE un-natural uses of voice. I CAN, and HAVE been heard half a mile....but it is NOT natural or good for my voice. And there are songs I have been singing on a regular basis for over 30 years that are uncomfortable in either the upper or lower range, not because I am not used to singing them,(as I have sung them frequently and regularly) but because though I CAN hit the notes I still, after 30 plus years have to FORCE them...

and as far as I am concerned, if you have to force it, it's un-natural. But of course that is opinion. I have lots of opinions.