It's not the guns. Switzerland has as many guns as the US and had 3 mass-shootings in 100 years.

[The Velveteen Ocelot]

32. It's the guns plus the culture that promotes worship of them.

In Switzerland and other European countries where gun ownership is common, guns are heavily regulated and licensed - and people think of them only as tools for a particular purpose, like hunting. In the US, though, there's a symbolism some people attach to them having to do with patriotism and, apparently, manhood. They are regarded as necessary not only for "protection," but as a means to solve problems because real Americans are strong and tough and if someone gets in your face you can just fuckin' shoot them. You also need more than one of them, even if you can shoot only one of them at a time, because, I dunno, the government is going to come and take them and then what? There's a super-weird mindset in this country about guns, and that mindset makes the damn things proliferate because we think everybody ought to be able to have them, any number and kind they want, and the more people that have them for whatever reason they want in order to solve any problem that vexes them, the more gun violence there's going to be.