I hope you have a daughter one day - only then will you understand this Dad. If you have one already and you don't get it - sorry for your daughter.
I would hope, as a father, I would be clear headed enough to call the police and report what was happening. This way I wouldn't need to wave my gun and possibly injure myself, my daughters or one of the frat boys. You seem to be under the assumption that everyone at the party knew who the girls were and that their father was looking for them. Hell, this was a party. A bunch of college kids drinking and having fun. How many people on this board went (still go?) to parties like that? Suddenly, some frenzied guy who nobody ever saw before, bursts into the house and starts demanding to know who's throwing an underage drinking party- what do you expect them to do? It's lucky they didn't shoot him. The guy's motives were pure, but his actions were stupid- incredibly stupid.