Well in this case the person accidentally made the invitation public.

I don't know whether your idea really helps much, because other times people intentionally make flash mobs, and they can be problematic. It seems to be difficult to address without totalitarian measures.

"Well in this case the person accidentally made the invitation public."

Doesn't Facebook make it possible to change the status or remove it, once she realized her mistake?

It does. In fact, she deleted the entire event. But by that time it had gained enough momentum for somebody to just make a new event and it was then totally out of her hands.

By the time you realized the mistake the invitation could have been copied elsewhere.

I think the problem here isn't Facebook, it's the incompetent and hysterical reaction of the police to those parties.

Where I live, an illegal Project X party descended into a riot a couple of months ago. The police were were rational in their behavior. They started to intervene once people started to climb on a bus stop's roof - those idiots were very near to power lines and could have been bbq'ed because of their intoxicated state. When the police tried to get them down the mob started to throw glas bottles at them. Alas, it quickly descended into a riot and the police had to disband the mob with tear gas and rubber bullets.

The entire vibe of the event was not peaceful, it was clear from the beginning that people wanted to start shit. After all was over the entire city's central place was littered with glas shards and trash.

2 months prior to the event thousands of people danced peacefully through another city, Bern, also during an illegal party, and there were no riots.

"Hysterical reaction" to a party where 3,000 people show up at a town of 19,000? That's asking for trouble.

Methinks you have too much faith in mobs; as expected, they smashed and looted. I suppose that was the police's fault?

Indeed. Even if the police over-reacted, which could mean anything from merely showing up to throwing tear gas, anyone in a mob is free to walk away. There is no obligation to throw bicycles at the police.

If you don't throw anything at the police, they may not tear gas you, and what fun would that be?

The police reacted as police do when outnumbered by an unexpected and unpredictable large number of people concentrated in a given location.

The problem is a person making a private party invitation public, while being naive about exponential growth as the invite is passed from friend to casual acquaintance to complete stranger to anarchist to criminal.

There's nothing wrong with protecting people from themselves. We do it all the time.