DovidM, have you ever read R’ Moshe Feinstein’s teshuvah on mechitzos? R’ Soloveitchik’s? The main point of the teshuvos is that the point of a mechitzah is to show a separation between men and women, not to hide the women.
As for the seating, having separate seating is a recent thing. When R’ Moshe Feinstein married off his children, there was mixed seating. When R’ Aharon Kotler married off his kids, there was mixed seating. Separate seating was just an additional chumrah that was adopted recently by chareidim, most likely taken from chassidim, who have been doing it for longer.