The absence of a main conjunction

Notes that understanding the necessity stated in "being necessary to the security of  a free state" as always true coming from the authority of writing a constitution does not give a good reason for not using a conjunction to connect to the operative clause. Actually saying something like :
Because a well regulated Militia is necessary to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed.
while would still be faced with the same question of if they did not want to restrict the operative clause by the first one why did not they put the operative clause first, the use of "is" instead of "being" would make a better case for a continuity claim regarding a  militia being necessary to the security of a free state. 
Understanding the necessity stated in "being necessary to the security of  a free state" as coming from the authority of reality and intended to reason with us, on the other hand, can more sufficiently explain the absence of a conjunction to the operative clause. Had the amendment been stated as, for example, this:

If a well regulated militia is necessary to the security of a free state, the right of the people...

it would have been still suffering from the same shortcomings of the comma-less before "being" version. That is because ,as mentioned earlier,the comma after being serves both the purpose of stating the necessity as a condition on a militia and also the purpose of stating that satisfying that condition is dependant on the environment in general and not the militia itself as long as it is "well regulated". The example above satisfies only the first of these two intentions.