there are rapists, murderers, pedos, etc out there that these people could use there time attacking
Best left to the police I think!
I think we're getting a bit carried away with this (especially as the original post is now several years old). These events are so rare as to be inconsequential. You're much, much more likely to be mugged on your way home tonight. In fact you're probably more likely to be mugged on your way home every night this week.
IF this does ever happen, pack up and go home. Don't be drawn into violence - that's always
the worst response. If you are actually attacked, you can use reasonable force to defend yourself so that you can remove yourself from the situation.
But, honestly, don't dwell on it.
And those who were seen dancing were thought to be insane by those who could not hear the music