If they can seize property on the basis of another's drug use, then I guess I am liable now. We found a mobile meth lab on our property a few years back. They come in thru private property, went up a stream bed out of sight on a 4wd jeep, built a fire and made a batch, then left the mess. Did not even know it till I was fishing up stream a week or so later and found it. We also had someone burn a vehicle on the same property one night, did not even find it till next rabbit season. Local law enforcement did not even bother to make a report.
Of course, we would be covered by a trespass law, the land is posted and they were not invited. Owner's of the event could be held liable. If you hold a party and let an underage person drink your booze, then you are liable. If you give a legal person booze and they have too much, take off driving, and kill someone in a wreck, you could be liable. This did apply to bars unless it has been changed.
I would assume there are other things involved in this than what is making the news. I read a little about it on River Hills Traveler. I would assume a crowd like this would draw may have had some ill effects on the local population. While most were probably upstanding persons, I would assume local law enforcement probably saw a spike in crime during the events. There is another event that draws this same problem over in Ill. at a Saltpeter Cave.