IMO, Bonnie said they were drunk: "Recently I attended an evening of music where I watched the performers drink a bundle. You could see they had quite a 'buzz going'." (The bolds are mine.)

In any case, what she was saying was that it interfered with her enjoyment. It's not about how much, if any, drinking is OK. It's about whether it bothers us to watch it.

Personally, I don't mind if someone is a little buzzed. Unfortunately, if someone's up on a stage and is drunk, my first reaction is embarrassment. I can't get that feeling of "oh shit - he's making a compete ass of himself" out of my head.