Not to mention that the National Guard can, with the stroke of a pen, be federalized and become part of the national military. If the Second Amendment was only about a "national guard" then the firearms under their control would, at the point of federalization, instantly come under control of the federal government.
The Second Amendment does not _grant_ an individual the right to own firearms. It _prohibits_ federal and state governments from passing laws limiting or outlawing the private ownership of firearms. That's why the term "shall not be infringed" is used.