I've never been to a meetup group, but if I were treated the way you were, I wouldn't go back.

Groups tend to have a personality, and this group's doesn't seem to mesh well with yours.

I agree with you; anyone who does not want to be photographed like this should be respected. It wasn't so much about the photograph as it was this woman asserting her dominance and the others backing her up. They probably would not admit to that, though.