If a folk club is running in it's own room it has as much rights to expect quiet from the audience if it charges for entry or not. Mind you, I suppose payment for manners would be an interesting concept...

Standards are irrelevant too (although may be of interest in terms of what is considered value for money when door charges are applied - dealt with elsewhere recently). In any case, in my experience, the "entry level" standard at the informal sessions tends to be higher than at an open to all singers night.