I don't think anyone has said a high voice isn't natural. If you have a naturally high speaking voice, your singing voice will be high too. But classical singers are often trained to extend their range as high as possible, which isn't a useful or appropriate thing to do for folk singing.
Singing with the head-voice (see Jim's post above) also makes the song sound higher in pitch than if the same notes are sung with chest voice. If you want an "earthier", less girlish sound, you don't have to lower the pitch or sing below your comfortable range, you just have to use chest-voice more.

Marje