It's a good point. And our society has changed a lot over the last few decades. People are much more sexually adventurous than they used to be.If you were in a room having sex with a strange girl and her mate let herself in and asked if she could join in, wouldn't you be well up for it?!
I would if she was attractive enough (and I was single). I certainly wouldn't have any qualms about the casual nature of it all.
A juror like Creaky could have a much different outlook than a juror like you, but the idea is that with 12, we should get a balanced view. But there's no guarantee.