I actually think onstage seating helps promote good audience behavior. First off, cell phones, bags that make noise, etc, aren't allowed on the stage (at least in SA). Second (from what I've seen) the people on the stage are aware they are on the stage and are much less likely to talk, sing along, etc with the show. If the whole audience sat on the stage, I think we'd have a very well behaved theatre audience.
But HAS anyone seen terrible behavior from anyone sitting on the stage for any show, out of curiousity?
"If there was a Mount Rushmore for Broadway scores, "West Side Story" would be front and center. It snaps, it crackles it pops! It surges with a roar, its energy and sheer life undiminished by the years" - NYPost reviewer Elisabeth Vincentelli