You are falling into a trap interpreting the National Guard as the militia. There was definitely no national guard at the time of the writing and adoption of the bill of rights. So construing the word militia to equal the national guard is a false argument because the concept did not exist. Militias were small local volunteer groups expected to provide their own arms. Hence the need for privately owned arms. The Continental Army was paid men from each state with arms provided by state coffers. Still not a national organization.