"Howitzers, for instance, are not protected. Nor are .50 caliber machine guns, among others." ?
Using Galen's logic, the only weapons that would be allowed would be muskets and swords. I believe the founders wanted any military weapon available to the people, who in fact, formed the militias. That applies today to any weapon that can be used by today's military as well as it did in the days of muskets and muzzle loading canon.