Notice how easily one crazy subject can manipulate and cripple the law enforcement activity in an entire region of the country. LAPD and many other agencies in the Southwest are suspending many day to day law enforcement activities due to the the manhunt.
And notice how quickly (understandably, in this case) law enforcement recedes into self-protection mode due to the actions of a single perpetrator.
Now imagine that, due to natural or unnatural emergencies, the unrest was widespread and imagine the complete absence of police protection that would immediately ensue. This is not a reflection on LE whatsoever, but an acknowledgement of the inherent limitations and folly of relying on police agencies for protection during truly exigent circumstances.
Yet, there is no reason why a citizen might need 30 round ammunition magazines.
Our sense of security is based on a historical relative normalcy that is far more fragile and fleeting than we realize, despite many moments of clarity that should inform us otherwise (Rodney King, Katrina, 9/11, Pearl Harbor for God's sake).