I'm with Texas Guest and Chris on this. I cannot see why it is unacceptable for performers to use music/songsheets. What particularly gets me is that those who insist you must learn the words are so often dogmatic about it and will even complain about using words at a folk club/singaround when the only "audience" are the other performers.

I do try to learn the words of the songs I sing as I have found that the effort of learning the words helps me to understand the song better and along with learning the words, I am usually working on how to present the song at the same time. But there are songs where I find I blank on certain lines and having the words handy is a great help. I find the same thing with tunes. I seem to go through a stage in learning a tune where I have the tune in my head but my fingers will refuse to behave and playing from the music makes sure I can play the tune through properly.

I recently apologised at a folk club night for using music to play a tune and was told in no uncertain terms I had no need to apologise and it was perfectly OK to use music.