The response is that the Supreme Court has ruled that the right is reserved to the people not to the states. The Bill of Rights applies to the people, only in the 10th does the rights of the States come into play. The 1st applies to the people, the 2nd to the people, the third to the people, the fourth to the people the 5th to the people, get the drift?
The right protected in the 2nd is the inalienable right of the people to keep and bear arms just as the freedom of speech and religion is the freedom of the people. It's not a conditional clause, it's an introductory clause explaining why the right of the people must be protected.