It's as simple as this: Someone (depending on their animosity toward others) gets a gun then storms a place where guns shouldn't even be a thing and this happens. It's happened at Sandy Hook, a grocery store in Buffalo, a Walmart in El Paso, and it just gets worse.
I have no intention of owning a gun for my entire life but that doesn't mean people can't have one for safety reasons. Shooting up a school or any other public place is violently pathetic, unreasonable, and should constitute life in prison sentences. I would demand the death penalty for some but to some extent life in prison is actually much more harsh.