Some posters here seem totally confused for terminology. A middle C is the C near the bottom of the staff with a treble clef if sung by a woman or played on a violin. Male singers will usually transpose that written note an octave down, so that the sound is no longer a middle C. The average male voice, called baritone, has its most comfortable range in the octave down from the middle C. Average female and young boys' voices have their most comfortable range slightly higher than one octave above. Therefore, the usual song and hymn books prefer that range, so that most people can sing easily, men and non-men one octave apart from each other.

Performers of folk songs (in a narrow sense) who want to sound as if they were ordinary folks will stick to that range, often encouraging their audience to sing along. However, there is a lot more to folkloristic singing. Many traditional styles require a sophisticated voice technique and long training. Some are reserved for people with suatable voice characteristic. For example, the seemingly highly artificial art of 19th century Italian operatic tenor singing has its roots in genuine folklore - reserved for such voices, and, yes, "loud" as if overwhelmed with emotion. Other traditions and styles have a preference for bass voices - think of "Russian/Bulgarian basses".

Bottom line for public performers: choose a style that suits your voice, and make sure to give it an adequate training.