I love how people are mad that you're right. The only technicality I'd add is that concealed carry is a thing, so you likely walk past people carrying without knowing it, but that's the whole point of concealed carry in the first place.

Mass shooting events like this are a social problem that ends up being very complex when you start to actually try and figure out why they happen and how to prevent them. There is no short answer, but Angry White Men by Michael Kimmel is a good place to start.