I disagree with the notion that an unaccompanied song has to be sung with a perfect voice,
perfectly in pitch. Many traditional singers have raspy and often "pitchy" problems though they are able to communicate the important aspects of the song.

People with good voices can sometimes be dull performers.

A good song remains, however, without damage to it by non-professional singers without vocal training.

This calls into question: what is a good voice? Here's another circular discussion.