Gun proponents use a lot of theories, and stubbornly ignore what people have already achieved elsewhere.
Mass killing is very very very hard to pull off without a right weapon. On the same day 20 children were killed in Connecticut, a man attacked a school in China. Only he had a knife. Everybody survived
Australia had a series of mass shootings. They implemented a gun reform, effectively taking semi-auto rifles out, and had no mass shootings ever since
. They also have much lower homicide rate than the US (just like every other developed country).
The theory that without people hoarding guns there will be more deaths is completely unsupported by facts. In the US, areas with higher gun rate ownership have higher homicide rates (I'm looking at you, South). Worldwide, USA has by far the highest murder rate among the developed countries. Every one of us, despite guns, is less safe than an unarmed German or Britt.