I believe, that while there have been many arguments going in all kinds of directions, that the most simple and straight forward answers are often the best and most accurate. When they wrote the Constitution they couldn't have envisioned very many of the things that have happened within our Federal Government and the restrictions that they have placed on our every day lives. Won't go into them as they have mostly been covered.
Republican/Democrat/Tea Party/Libertarian - doesn't matter, the Federal Government has way overstepped their bounds because "We the People" have allowed it too! The 2A was designed to allow the people to protect themselves FROM the governement! When it got too radical and the elected officials stopped listening to "We the People", it was time to change the people representing us. Nowadays we do it in a "civilized" manner through elections, but back in those days, maybe not so much. They gave "We the People" the power to use whatever means necessary to take control of the government back, to the people. That is the part that our elected officials have forgotten, they are there for "all the people" and not themselves or their special interest groups!