Context also matters. The authors also thought that a standing army was part of the park to tyranny, opting for a militia system in place of it. The purpose of the Second Amendment, by its own words, is to ensure that nothing could legally stand in the way of regular and irregular militia being able to protect the fledgling nation.
As it stands now, the Second Amendment is an anachronism that's sole purpose for existing is no longer applicable. It needs to be re-evaluated and amended to fit the needs of a nation that has both a standing army and a problem with civilians shooting each other (police are civilians too).