There's no justifying this, just another overextension of police power into our lives. A court just recently decided to include "expressive dancing" as a method of protest and effectively banned dancing at memorials like Jefferson's (which is hilarious, because if Jefferson were alive to watch this video he would be ashamed of our government and want the law removed instantly). These people planned on coming to dance in protest of the ruling... so in a way they came there to get arrested. But the cops had no grounds to handle the situation like they did.
Dancing is one of the purest forms of human expression, so I'm baffled by the fact that the court thinks they have a right to ban it anywhere. Add it to the list of bullshit laws I suppose, seems to be growing every day. Welcome to the USA, were you'll get by just fine as long as you agree with us at every turn and never EVER question our authority... pretty damn sad that people aren't angrier already