They are tools of the rioters. And yes, the mobile networks in the local area of a riot should be turned of. Not one of my posts has said social networks are RESPONSIBLE for the riots.
Regardless if it's Twitter ( and there are some examples of people using it including 2 arrested in Kent ) or Blackberry, the networks should be shut down.
I don't consider it evil - indeed it's helped the fightback by Londoners but in this instance it surely would help police if it was blocked for a couple of weeks ?