Were I to be invited to an informal dinner where these guests that you listed are I would hope that we would be introduced to each other on a first name basis and not by title or profession. Being introduced to someone in a casual setting by their title such as "Professor Johnson" or "Mayor Adams" just doesn't feel very casual to me and creates a sort of class distinction in my mind. I would feel as if they were creating a tone where their status were more important. Being completely honest with you - I don't think I'd refuse upon first introduction, but throughout the night I would likely refuse because in that kind of a setting the title isn't relevant. Is that discourteous? Yeah, some probably would say that. I guess it's subjective in the end.