Mother Jones has a comprehensive list of myths and subsequent debunkery. Some highlights:
Myth #4: More good guys with guns can stop rampaging bad guys.
Fact-check: Mass shootings stopped by armed civilians in the past 30 years: 0
• Chances that a shooting at an ER involves guns taken from guards: 1 in 5
Myth #5: Keeping a gun at home makes you safer.
Fact-check: Owning a gun has been linked to higher risks of homicide, suicide, and accidental death by gun.
• For every time a gun is used in self-defense in the home, there are 7 assaults or murders, 11 suicide attempts, and 4 accidents involving guns in or around a home.
• 43% of homes with guns and kids have at least one unlocked firearm.
• In one experiment, one third of 8-to-12-year-old boys who found a handgun pulled the trigger. [...]
Myth #8: "Vicious, violent video games" deserve more blame than guns.
Fact-check: So said NRA executive vice president Wayne LaPierre after Newtown. So what's up with Japan?