Marje does make a good point. I have sometimes hesitated when it comes to introducing friends to folk music because I have inwardly cringed at the thought of their comments on some of the truly dreadful floor singers one gets.
It does seem to be unique to folk (though poetry slams are not far off) - jazz, blues; almost any other style seems to demand a degree of competance and commitment from a would-be performer. The 'good enough for folk' mentality is hard to shift from traditional music, however. The folk world is so bloody, maddeningly, uncritically tolerant (except, of course, of intolerance!).