Just how many people realize that ‘X being necessary [comma]’ is just a fancy way of saying ‘If X is to be necessary [comma]’? They really ought to learn that. Even Jeralyn Merritt claims this is an ‘individual right’ to keep arms, when if read correctly as English it means, simply, that the electorate could, for example, vote to hand out bazookas if the US were being invaded by, say, an army of bottlenose dolphins like on the Simpsons.
Of course Bush would federalize everyone and send them to Iraq, leaving himself as the dolphins’ human puppet.
Update: Maybe ‘if’ is not the best translation into modern everyday-speak. I wonder what grammarians call it, but in any case what you have here is a contingency relationship, plus also what you have is the right of a community to form a militia, which may or may not involve individuals packing heat. The weapons could, for instance, be kept locked in an armory and handed out in an emergency.