This has already been discussed, and though I don’t lump you in with the left, they use the “nuclear bomb” and “bazooka” argument to justify banning semi-automatic firearms.
The key word is “arms”. “Destructive devices” like NBC weapons are not “arms”.
Basically “the line” is set by the military.
Whatever weapons the common infantryman uses should be available to the citizen.
Thanks - perfect answer.