You conveniently leave out the advance of technology, and those good gentlemen were unable to forecast the type of future weapons that would be available and in the hands of people who not only might want to control the government (against the wishes of the majority)--they might even want to control you.
That works both ways, Bob. The Founding Fathers also couldn't have forecast the future weapons that would be available to an invading army or a domestic government that seeks to oppress the American people. Most people who share your viewpoint on guns consider the constitution to be a living, evolving document. If you hold that view, then you cannot, with credibility, say the First Amendment has evolved to restrict prayer in school and prayer at graduations, but my liberty under the Second Amendment has never evolved beyond an 18th century musket.