Quite a lot here are, in fact, amateurs..! As a 'pro' drummer, though, 'back in the day', I had a music stand propped up beside the hi-hat, supporting a ring folder full of several repertoires, drum scores I'd written out for the various variety stuff I'd be asked to play at the drop of a hat. I didn't 'read' from it in real time (no time, you see...), but it gave a quick visual cue as to what was to be played, and maybe a note or two (brushes with this band, sticks for another; stuff like that...). Amateurish..? Quite the opposite, for many situations. Sounds a bit 'snobbish', to me, anyway, to say 'Never on my watch..!'. If the presence of a music stand is all it takes to condemn a band/singer/bassist, there wasn't much respect for 'em in the first place.
I'd agree that it's not good for a singer to be reading from the book, generally, but having a music stand, in itself, is no big deal, for any band or occasion. Not knowing one's stuff is a different affair, and I wouldn't confuse the issues.