“Why” is a terrible word because it’s overloaded. Often when we ask “why” we mean “for what purpose” — we’re looking for intention. In the bigger questions (bigger than one person’s decision), that doesn’t make sense.
“Why do we let people buy those dangerous guns?”In a system the size of our country, there is no “for what purpose.” Outside of monotheism, there is no singular man-of-will deciding, the system is wider and more diffuse than that.
Perhaps we mean “how did it come to be”? how did the system get to this place? then we can go back to the 2nd amendment and tell a story about British soldiers and their muskets. In other cases, there isn’t a solid story, or the one that exists was made up in retrospective. Randomness happens, and the system can reach various states without any reason for getting there. As my mother-in-law says, “Things are the way they are because they got that way.”
A more useful question is “how does it stay true”? We aren’t inundated by British soldiers with muskets anymore. The original reason has passed on. If we cared about defending ourselves from the government, we’d guard encryption and privacy. How does it stay true that we let people buy those dangerous guns? and then you get to the NRA, gun culture, and the elements of our society that keep guns legal even when they cost oodles of innocent lives, with none of the original benefit.
Asking “how does it stay true?” gives us some hope of changing it.