They are protected by the full faith and credit of the United States and preventing default is no less justified than using American military power to protect against an armedinvasion without a congressional declaration of war.
The first is that although the West is safe in the sense that the existential threat of invasion by a malevolent foreign power or a first strike by a nuclear-armed aggressor is now vanishingly small, the rise of jihadist terrorism has left people feeling vulnerable.
It appears that, on reflection, the Wyoming House of Representatives has decided the risk of invasion by its neighbors is remote enough that it can do without its own armed forces for now, and in particular does not need to consider whether an aircraft carrier might come in handy.