Look, lets get this "words on paper" thing straight...

There is a HUGE difference between:
(1) learning a song (really learning it) and taking a crib sheet in case you forget the words,
and
(2) not learning a song at all, and reading it all, - no question of forgetting the words because you've never learned them in the first place.

It's the same with all other technique whether playing an instrument or singing. We don't all have the same abilities or skills but we do owe it to our audience to spend some time at home practicing what we do to the best (or something approaching it) of OUR ability.

It's elitist to put down somebody who's basically not very talented but is making an effort, and IMO it's quite right to chastise someone who quite clearly can't be arsed to practice or learn anything and is wasting everyone's time.

Even the most musically illiterate audience member can tell the difference. It's not about how good you are, it's about how much effort you make.

(I think I posted something like this earlier, but it didn't seem to stick)
Anahata