PA... the links you've provided aren't for flash mobs. Here you can find out what "flash mobs" are. This is an example caught on video, and this is another, and this is another.
Regarding the one article from WLS questioning whether the beach overcrowding was related to a flash mob... well, I think the author just didn't know what a flash mob is, either.
Use of cell phones to create a melee- a near riot... acts of violence. What is that called? Anyhow it is getting old.
Disruptive? Violent? Criminal? Bad behavior?
Although I will admit some feel flash mobs are disruptive and bad behavior, too.
Riotous behavior has been old, PA... for a long time. Modern media and the internet is just making knowledge of events (present and past) much more readily available.
In other words, I'm not sure that these things are happening any more than they used to... we're just hearing about them more.
Try turning off the tv and computer for a month or so. You'll be surprised how much better your life will be. [:D]