Little evidence links mob violence to social media

Social media's role in the UK riots

STORY HIGHLIGHTS

• Term flash mob has become associated recently with sudden, violent group acts
  
• The phenomenon has spread to big cities in the U.S. and elsewhere
  
• Social-networking tools have taken the brunt of blame despite little evidence
• Many efforts to block social-media activity are unconstitutional, experts say

(CNN) -- This summer Cleveland Mayor Frank Jackson has wrestled with one of his biggest challenges since taking office five years ago.

Worried that flash mob violence would overrun city streets as it had elsewhere, the Cleveland City Council unanimously passed legislation that would criminalize the use of Facebook, Twitter and other social media for assembling unruly crowds or encouraging people to commit a crime.

But Jackson, after consulting with advisers, defied the council and vetoed the ordinance -- his first use of that power as mayor.

"It's very difficult to enforce something that's unconstitutional," Jackson said in an interview with CNN. "To make a criminal activity of just having a conversation, whether some acts of criminal activity are associated with it or not, it goes beyond reason."