First point:-- If you listen closely, not very many singing voices do not have at least some vibrato. It's actually a sort of unconscious cybernetic feedback mechanism that helps a person stay on pitch, and if you sing much at all, it developes naturally. People whose voices are completely devoid of vibrato tend to sing flat.

Second point:-- I think we have a double-standard here. Joan Baez sings in her natural voice (her vibrato would have developed whether she tried for it or not). Almeda Riddle sings in her natural voice (her voice has a bit of vibrato if you listen carefully). Some people would say that Almeda Riddle is real, Joan Baez is not. Yet, the way both of them sing reflect the musical influences they grew up with. These same people would also probably say that if Joan Baez suppressed her natural soprano and tried to sound like Almeda Riddle, she would be more "real."

I leave it to you to work out what an idiotic concept this is.

Don Firth