This is simply a myth. A gun purchased for protection is far more likely to kill the owner or relative. When was the last time you ever read where a mass killer was stopped by someone with a gun with the exception someone from law enforcement.

“It can work both ways,” said Pollini, who also worked 30 years as a New York City cop. “In one, you have law-abiding citizens present at the scene of a shooting that could terminate it, assist in apprehending the individual."