EEEEEk RP you have got me completely wrong here. I was trying not to put any prejudice on voyeurism if that's what you're into. Remember there was very little back ground given in the original post.
"poly negative" feelings: I thought the fact that she was having a physical rather than emotional response might be because she felt that she had been included, and her partner was reassuring that she didn't feel able to share any negatives that she was feeling about the whole thing.
In no way do I think that watching intimate sexual acts is necessary, wonderful or everyone's cup of tea.
Hope that clarifies.