I think it all stems from the time when 'folk-songs' didn't exist!
I mean the days when 'Fred' would rise from the corner of the Tap Room in his local pub and give a rendition of 'his' song. I have found many instances of certain songs being assigned to certain singers and woe betide the young upstart who dares to attempt 'Fred's Song'. The tradition continued well into the last century in the form of family sing-songs around the piano where everyone had 'their' party piece. This tradition appears to have continued to the present day in the Folk Clubs. However, this can be shield behind which those too idle to learn new material can hide. Those with a jealously guarded small repotoire are the easiest to upset.
My approach is that in my local, regularly visited clubs, where I know most of the members, I wouldn't sing anything I know is regularly sung by another.
On visiting a new club or festival anything goes.
As regards the 'giving' of songs I can agree that in the context of family songs as outlined in a previous mail it would be impolite to use the material and would probably result in a family feud.
In the folk club situation I would say that no-one has the right to 'give' songs unless they are the author and even then, in these days of copyright litigation, it is important to specify exactly what is being given.