GSS ..."Nobody took away your choice.
In fact one of the clubs that restricted choice of folk music was The Singers Club its rules were proscriptive, the dictionary definition of proscriptive is imposing restraint or restriction, thus restricting or taking away choice."

I suppose that cuts both ways.
If the rules coincide with what you enjoy hearing then it means the whole evening might be bliss. And you know to avoid it if the style doesn't suit.
But I'm not sure if I'd prefer
an evening of good/bad/mediocre performers sticking to the style rules
... or an evening of mixed styles from good performers.
Though, not being an organiser, I don't know how they restrict the lesser performers for either format.

~~~~~

Les in Chorlton Jan 7th 
Yes

and
Good beer
Friendly barstaff
Warm in winter
Cool in summer