The "flash mobs" in Philly are violent. They are not just stealing they are beating up random white people that they view as easy targets. The reports are that they are ALL African American youths, mostly in their teens. Several people have been critically harmed, some permanently.
Firearms, may or may not be effective in keeping you and your family safe. That's the bottom line. Keeping you and yours UNHARMED. I have been carrying pepper spray in addition to a firearm as I believe that could be the best way to deal with a crowd and give you time to get away while not bringing the wrath of the urban legal system against you later.