Well why not close the internet temporarily? Why not turn off the mobile networks? This is absolute nonsense. Social networks are methods of communication, they hare not RESPONSIBLE for these riots.
Do you really believe this? Because an infinitesimally small number of people use it to organise a riot it should be shut down?
Do you think that anyone uses e-mail or the phone to cause trouble? Should we close them down too? What about the internet generally, there's loads of nuts everywhere...