There used to be an institution known as a 'hootnanny'...we have all seen the word, but not everyone has been to one
In the early 60's, I actually attended sessions which were CALLED 'hootnannies', and they differed from 'song circles' in a couple of significant ways
1. No one HAD enough books to read from...indeed we had very few printed sources, and we knew significantly fewer songs, so we tended to sing from memory, no matter where we had gotten the songs.
2. These sessions were NOT democratic & equal opportunity. The people who knew the most tended to do the most, and newcomers were sort of expected to sing along, learn and add stuff as they developed a repertoire. This is a bit intimidating in some groups, but if you do it this way, you end up really KNOWING some songs and learning how to fit in.

Song circles are nice...they give everyone an opportunity, but they also test the patience of the better and/or more experienced singers- and when the use of RUS and such is the major format, I think they tend to drive away a lot of better singers who simply get bored with reading out of books (and especially the ONE BOOK).
There is no easy solution for this...in a 'hootnanny', the "in group" must work to give the newbies some help & opportunity. (I have been in groups where 3 or 4 people managed to eat up an evening singing back & forth, showing off their repertoire and barely recognizing the existence of anyone who did not know how to 'break in' with that exquisite sense of timing & taste one needs in such a group.(I myself am in the middle area...I know a bunch of songs, but am NOT a recognized guru...I have been in both positions, depending on the composition of the group)

The point of all this is, that total equality and democracy and use of 'bibles' can develop cameraderie & be a lot of 'fun', but does a very limited amount to really teach & educate; while an occasional 'hootnanny' format can open the eyes of the newcomer and give them a sense of what is possible, even though it requires some forbearance to make it work. If the personalities in your groups allow for some of each, and if these issues are openly and honestly discussed, I think the appreciation of folk, folk-like, and other music can be greatly increased