A different picture of the Notting Hill Carnival

If you heard about the famous Notting Hill Carnival that took place last weekend from a policeman who was working there, you would get a very different picture of the event to the one painted by the media. There was a lot of crime: cases of mugging, pickpocketting, fight, stabbing, rape and so on. The offenders were mostly young people from the gang culture... What brings about such uncivilised behaviour? Is it mainly the result of stress-free upbringing, media and pop-culture influenced?