This contribution from Jim Bainbridge reads like a breath of fresh air to me. I agree totally with everything that he says.
One Jim writes:-
I would find the practice of including them in a folk song evening dubious
and the other responds:-
I would contend that such tunnel vision is nonsense.
and I would have to agree with the latter opinion.
I am probably wasting my time here but let me ask what I think is are two important questions:-

* When did folk songs become fragile flowers that had to separated from all others and only performed on their own away from other music as if they were museum pieces?
* In all the contacts and encounters with traditional singers and musicians (probably amounting to thousands of meetings) that Jim B. Jim C. and Vic S. have had outside of folk clubs, how often have traditional songs & tunes been in a 'siphoned off' situation?

My answer to the the first one would be that folk song is robust, Its strength is in its fundamental functionality whether this is in telling a story, describing feelings or situations that the listener can empathise with or fulfilling a convivial or ritual role. Folk song and music is strong and can hold up its head in any company.

My answer to the second one would be 'none or very few indeed'. Yes the singers usually realised that difference and the value of traditional items and might not bring them out in every situation but they lived in a world where there was a great deal of other music, some of it very good indeed and they would adopt some of it and here, as Jim B. has suggested, is where style comes in. It was what the Copper Family brought to the singing of Mills Brothers songs, what Jane Turriff brought to the songs of Harry Lauder and Jimmy Rogers, what Irish travellers brought to Country & Western etc.etc. that was interesting.