Flowcharting Mass Shootings here in the U.S. and on earth

I liken it to lemmings jumping off a cliff when there are too many of them like in a Disney Documentary I saw once.

Here is my flowchart:

There are too many people.
Some people cannot deal with this and so think: "Who can I kill to lessen the amount of people on earth?"
They direct their anger towards another religion or nationality or another race or skin color and decide to kill some people.
They buy weapons legally or illegally. I'm thinking it doesn't really matter whether their purchases are legal or illegal (at least here in the U.S.) in the way it makes sense.
They go and kill people (and within a minute or 5 minutes (depending upon how close law enforcement is) someone shoots them or takes them prisoner and if they are alive they spend the rest of their lives in jail.

But, how many others who see this on the news are driven to do the same thing like Lemmings? It's sort of like an ongoing chain reaction of mentally disturbed people who don't like overpopulation here in the U.S. and around the world.

Is there anything that can stop this here in the U.S.?

I'm thinking the ONLY thing that makes any sense is for people to arm themselves to shoot these people before they kill so many people.

This to me is the only thing that makes sense in actually stopping someone like this in reality (and not  just in someone's group fantasy).