Even if a folk club is 100% trad, you're not going to be hearing Traditional Singing, just a load of middle-class revivalist hobbyists having a good time at the expense of a culture from which they're a million miles removed in socio-economic terms.

You're right about folk clubs being a highly artificial environment for the recreation of something which originally flourished in totally different settings. But as far as class is concerned, I think it's best not to prejudge your audience & fellow-singers - and certainly not to assume that there's some other pub down the road which is full of real authentic ordinary working people. Folk events (of whatever sort) attract a tiny, highly unrepresentative fraction of the population: it's the fraction of the population who are interested in folk (of whatever sort). As for whether they grew up on a trust fund or free school meals, you can't really tell without asking, can you? DA,DT,DK,DC I say.