"No one needs an AR-15 with a 30 round magazine", "it can't happen here".
During the LA riots after the police were acquitted of beating Rodney King the police were pulled off the streets. Something like 50 people were killed. Korean shop owners used AR-15's to defend their businesses.
In 1800's Montana, the Sheriff (Henry Plummer) was lynched for being the leader of a gang that was robbing and killing gold miners.
There have been numerous times in the USA history where plain folks could not depend on their government to protect them.
"One man with a gun can control 100 without one. " - Vladimir Lenin