M.Ted "Wouldn't it be nice if everyone knew the words to every song you wanted to sing? Wouldn't it be nice if they spontaneously could join in in whatever style and whatever key anyone wanted to start in? ...

Really,it's really good that you can find people who get together to sing anything at all. Most people don't sing together. Most don't know the words to anything in particular, and most can't reliably sing a melody unless there is an oldies station playing. The books, which ever Blue Book you happen to have, are a blessing because they make it possible for more people to participate--"

Hear, hear, Ted.

Mary, I'm actually in neither "camp" completely.   (Maybe that's because I'm pretty strong on both visual and auditory processing, though probably leaning towards auditory, especially when it comes to the music, as opposed to the words.)
Nothing gripes me much more than having the group screw up the phrasing -- not to mention the feeling -- of a song because they're leaning so heavily on the "crutch" of a piece of paper and can't watch the mouth of the songleader or the hands of the rhythm instruments and don't even realize that they already KNOW most of the words to the freakin' song already!
But something almost equally frustrating is doing a song where a group of voices would sound way better than a solo and some harmony would raise the experience to a whole new level -- and for that not to happen because only one person knows the lyrics!
(That's a common experience I have in some bluegrass groups, where I find myself aching to hear 3-part, tight harmony, but we have no lyric sheets.)

I would add that I get pretty tired of being 'instructed' to "please choose songs that have choruses so everyone can sing along."   Well, a lot of wonderful songs don't have choruses.

And it's unrealistic to expect a "group" to learn anything but the simplest songs by just hearing them in a song circle a few times a year (if that).    You can take your books or song sheets with you and make a point of learning the lyrics if you like. (You could do that with CDs or audio tapes, too, but people seldom have a batch of those to hand out -- and they almost never use them DURING the session.)

For me, the best possible scenario is where people come to think of books and song sheets as learning devices for new material and as sort of like "training wheels" for use while you're learning a new song. Kind of like being in a choir, where you rehearse with the hymnal or sheet music, but you hold your music up just below eye level and watch the choir director over the top of it, glancing down only as needed to keep your place in the music or trigger your memory of the next line.   And by the time you perform the anthem or cantata, you're hardly using that sheet music at all, even if you do have it in your hands.

G