Again: you're simply wrong. Slaves, immigrants, and women were barred from all rights within the lifespan of the founders. If you extend your argument, you can say that the freedom of the press wasn't a right either, since slaves, women, and immigrants didn't have the right to read or publish what they wanted.
The problem with this view is that the body of the constitution already gives government the power to raise and arm and army, and to enact taxes to pay for it. There's no need for an amendment to say that the gov't has the right to be armed when that right was already stated. It's redundant. You could, perhaps, argue that it's a right that was being reserved for the states, but it doesn't say that the states have the right to militias, it says the people. Moreover, the remaining nine amendments that form the bill of rights all concern individual rights, or individual and state rights (e.g. 10A). It would be very strange to see an amendment that not only says "people" but means "states", and is the only amendment in the bill of rights that applies only to states.
Take, for instance, the National Firearms Act of 1934. It was originally going to be a ban on handguns, short-barreled rifles (because they were effectively handguns, and would circumvent the ban), and machine guns. It was turned into a tax because lawmakers were pretty sure that a ban couldn't pass court review--while a tax could, since it was an enumerated power--which very strongly implies that it was recognized, even in the 1930s, as an individual right, rather than a right that existed for the gov't.
I could probably come up with a list of references if you were interested in reading more. I would not suggest anything by Michael Bellesiles, because his historical "research" was found to be deeply flawed bordering on outright fraudulent.