I rather liked this comment by "AllyF"
There's a widespread myth that law and order is preserved by police, politicians and other forces of authority. Not true. Never has been. If we all decide to go out and chuck a dustbin through Argos's window and help ourselves, it would take about 15 million coppers to contain it. We actually have about 150,000.
Law and order is kept by a collective acceptance of mutual goals. If, as a society, we look after each other, offer everyone a share and a stake in the common weal, maintain some semblance of a Rousseauian Social Contract, then the vast majority of people will mostly stick to the rules without ever needing to see a police officer.
When people lose that sense of being looked after, no longer feel part of society, no longer feel like they have any kind of share in any kind of collective, the ties that bind begin to be broken.
Rioting, especially the type of vandalism & looting we've seen in London, is a sure sign that the social contract is unravelling around the edges. In the days and weeks and months to come, we shall see how far it has frayed.
There are few things more dangerous to a society than a populace with nothing left to lose.