Any time there is a gathering of people, there are going to be incidences that get attached to the event. It only take a few people to give the event a bad name.
As a society, we have become too tolerant of riots and looting for that matter. Not too many years ago, reading the "Riot Act" was a prelude to deadly force. And, the penalty for looting under martial law was death. As harsh as this sounds, you wouldn't have to kill too many before all the assholes dissappear, never to return.