Without strong social incentives and harsh social punishments for deviation from these structures, they collapse – and they collapse because they simply don't serve large swaths of the American population (women who want equal rights, people of color, immigrants, poor people, non-Christians, gay people). There isn't much of a reason for why these particular structures are the best, other than that the few people who benefit from them seem to like them. But the fundamental argument in their favor seems to be that without a social organization that puts white Christian men on top, the hordes of "bad" people will simply be out there – and there is nothing we can do other than arm ourselves against them.
That's why "guns don't kill people, people kill people" is still considered an actual argument. It's why the debates on gun control go in circles. One side thinks we have serious but fixable cultural problems with violence, with a masculinity that is tied to aggression and with the glorification of gun culture, and that the wide availability of all sorts of deadly weaponry in such a culture enables an unconscionable amount of lethal violence. The other side thinks people are just sinners, our time on this planet is meant to be trying and ugly, guns represent freedom and man's dominion over the Earth, and gun deaths simply result from a lack of Christianity and the attendant breaks from a "traditional" model that necessitated the oppression of a great many Americans.
~ from The Conservative Philosophy of Tragedy: Guns Don't Kill People, People Kill People by Jill Filipovic ~
A gun in a person's hand turns them into a god. You get to decide who lives and who dies, who is granted mercy and who revenge is exacted upon. Maybe this is why fundamentalist Christians, in particular, have a love affair with the free access to weaponry. They are tired of being the ones under the thumb of the almighty -- knowing that one wrong move punches their ticket for hell and damnation.
Their narrow belief system doesn't allow them to feel free and unfettered. But a gun WILL do that.