Don't let a few negative comments discourage you. In folk music, as in other fields, some will like your style and others won't. I would think an unusual voice (especially if it's good) would be a plus. Who wants to sound like everything else? I have seen singers who were so into showing off their voice that the song got lost, and that's not good in folk music, but I would suggest recording yourself and listening to it. If you're happy, feel that you're getting the song and its message or story across, and others do appreciate what you do, then go for it. It's better to have an unusual voice that draws attention than to have a mediocre voice that is indistinguishable from everybody else.