To paraphrase 'Different Strokes for Different Folks' , it depends on the Attendees as to how a club (or session) functions ! Uxbridge USED to have a 'Singers get in free' policy , until it was two thirds of the attendees were wanting to sing !
The same goes for Maidenhead - On Singers and Musicians nights we regularly applaud the Audince ( BOTH of Them ) . If we performers got in free , the club would have closed YEARS ago .
I work fairly regularly for fairly serious money , doing stuff that I MOSTLY learned in Folk clubs , so all I am doing when I 'Pay to Sing' at a local club is RE paying what Folk has given me .
To any one who is fortunate enough to get enough audience to be able to book the occasional guest , and NOT charge Floor singers , I say "Good For You!" but there is NO point in having a slanging match because someone else runs a club in a different fashion !