I think everbody can sing - no learning required. The end product might be vitually inaudible or have everyone running for cover and set all the neighbourhood dogs barking. I think the question is really "Can training/practice improve this innate ability ?". The answer has got to be yes, but how far depends on you own musical sensitivity and even more on your motivation.

Folk music is a medium that will allow a much wider variation in quality of singing than most. I have always believed that "Telling the story" is more important than producing beautiful, but incomprehensible, sounds. The skills of delivery and phrasing can make up for all sorts of deficiencies in pitch and tone. If you are singing in public, projection is needed, but if you will be using a PA, not to such a great degree. Careful choice of material is VERY important - choose songs that will suit your voice/style, not just songs that you like someone else singing.

In order to sing, you must want to communicate with an audience. Performing of any kind is an ego-trip and to some extent a control-freak thing - if you don't see it that way, then why do you want to do it in the first place ? Keeping this in mind, try to develop a style and repertoire that best helps you to achieve this.