What will happen is the government will put in place more limitations, or loss of freedom on law abiding citizens. Same as they are doing on gun control. If there is a big enough outcry over flash mobs, they will react by installing cameras on every block, at a minimum. Of course the authorities will only react to something caught on camera that is easily handled, like jaywalking. Flash mob sighted will be a slower response, or any large gatherings cannot be acted upon based on profiling, until the mob is in action.
That's probably correct, plus we will have fewer stands and other businesses, goods behind barriers and panic button type defenses. Civilization will continue to degrade.