If we are to accept that guitarists should either give up or stay in their bedrooms until they have been examined and passed as suitable for accompanying songs, then I can't accept that; that would be true for any instrument. In fact, consider how well most unaccompanied singers deliver, both current (revivalists) and past (traditional). Should they be or have been prevented from singing in case they tarnish the jewel? As Martin Carthy has famously said, "the only way to damage it is not to do it". The beauty of folk music is that it gives people the chance to indulge in their inheritance irrespective of how good they are at it. The important thing is to respect the material, not to leave to those who are considered to be good enough - who would make those decisions anyway? An elitist panel?