Sounds to me like your critics are taking themselves too seriously. If you love singing, then sing. My personal opinion is that, if you're prepared to work hard on it, some of the things that you think you lack are probably within your grasp. My brother was tone deaf til the age of 22 in a family that was always very music oriented. When he picked up the whistle, I thought he would never be able to play. Now he can sing in tune, play more instruments that I know what to do with, runs a celtic band and session group and even teaches in schools.

You're lucky to have a natural gift in terms of your voice quality, but you should never underestimate the value of hard work, even in something as romanticised as folk music.

Cheers

Al