It wouldn't surprise me if overzealous enforcement of '21-to-drink' may have played a role in the festivities.
A kid knowing that he's about to be busted might be tempted to 'pound it down' before the heat arrives, and quickly get loaded, with all the problems that that entails. If an 18-through-21-minus-1-day-year-old wouldn't feel the need to 'look over his shoulder' for the fuzz, chances are that the party may have remained friendly and calm.
Hon, someday, when you grow up, you'll want extreme overzealous enforcement of such law because you won't enjoy drunks coming into your neighborhood and endangering your home and family.
Plus, they pee all over the neighborhood like animals.