To clarify some of this with more accurate info...
Seaside wasn't shut down at any time of night. Seaside instituted a curfew on the beach earlier this week whereby anyone under 21 was not allowed on the beach after 7pm unless accompanied by their parents/adult party.
I think this sort of backfired because it pushed many of these kids into Seaside itself. The main square turned into a complete zoo of pissant kids.
In response to that, Seaside and Walton County PD instituted a new plan on Weds night whereby minors were not even allowed in Seaside after 6:45pm without being accompanied by parents. It put an immediate halt to the chaos in Seaside
Atlanta gets undue blame for this week. Yes, it's when all the Atlanta folks visit for spring break, but it's also the most popular spring break for every school system in the region. One of the biggest issues in Seaside on Tuesday was a group of boys from Lexington Catholic HS in Kentucky - that group was beating people up randomly. Arrests were made.
Regarding private beaches, that's the new debate on 30A as many beachfront homeowners have begun policing their sand. These owners technically do own the sand to the high tide line. Only the "wet" sand is public beach in front of homes in Walton. (Bay County/PCB uses public money to renourish beaches so public beach is 30 feet beyond the high tide line - Walton doesn't renourish at all). This all started with Mike Huckabee in Blue Mountain Beach a few years ago. He was a major league asshole. Thankfully he's sold and no longer lives there. But it's becoming more prevalent among owners even though cops have publicly said they don't plan to enforce it, many have hired private security. You'll see signs and even ropes on sand now, too.
The biggest issue with 30A crowds of late is too much development has occurred. The huge increase in rental inventory has lowered the price point, which has brought in more visitors, but also lowered the demographic. There used to be limited inventory, and all fairly high-priced homes very close to the beach. Kept things quiet and a higher profile of guest.