I saw the amateur videos of HASC 26 on Gruntig, and the girls were having a really good time. And the reason why the girls were rocking is because of 'separate seating', as opposed to mixed seating (MBD only takes separate seating). If there was mixed seating they could never act like this. You can't be yourself; it's always "what will they think?"
And besides that you can't be yourself, co-ed also breeds sadness, because it's always "how come I can't get that girl, or such a pretty girl?" Or "how come I can't get that boy?" That's why there are no happy boys at a Litvish "vort" unless they get stoned. "Yoooy! Nekaayyves!"