I think you're saying the same thing as this, but, to me ... The prepper fantasy clearly says more about the ethics/ideology of the person having that fantasy than it does about what a crisis-society looks like. By adopting that lifestyle they're basically giving an early look at how
they might behave in crisis, and how they see their fellow man.
And I think you're right; if you look at how people behave in times of flood or famine, they do tend on the whole to come together.
From the outside looking in, I think in part it has to do with the history of parts of the US as a slaveholding society. In a society where a large minority (or in some places even a majority) are under the thumb of coercion, when order breaks down, there will be reprisals and violence. And I think this history has formed a cycle in some parts of the US long after the end of slavery, and also informs a lot of the gun ownership self-defense fetish there. e.g. for me, growing up in rural Canada guns were just a rather boring part of life because people hunted or had farms. But since then the have clearly become a kind of shibboleth, or cultural marker. Gun ownership is apparently at an all time high but actual hunting for meat is at an all time low.