several of those who sing unaccompanied do so because they feel they can't play well enough.

On the other hand there are those who sing accompanied because they feel they can't sing well enough - "And I think I'm a better guitarist than I am a singer - mind you, I would only ever describe myself as a 'competent' guitarist!"

I think Jerry's got it right there about the way that "singing some songs unaccompanied allows a freedom in phrasing and emotion that a regularly metered accompaniment may tie down." And let no one dare say that Jerry can't play well enough!

True enough people often enough feel they can't play well enough, or know they can't play at all. But that really isn't any reason for them not to sing, or for anyone to assume that singing without musical accompaniment is somehow to be defined as second best. It's different, that's all, the way that a solo singer is different from a choir, or a solo instrumentalist is different from an orchestra or a band.