The Founding Fathers were fallible humans, just like the rest of us. The Second Amendment, when it was included in the Bill of Rights, was probably a necessary thing; however, in the 21st Century, it leads to massacres like Aurora and Newtown more than it does anything to help "the security of a free state".
With repeal, firearm ownership and regulation could be reverted to the states, allowing for more flexibility state to state or even city to city.
We have changed the Constitution and the Amendments before when they have been overtaken by changes in technology or circumstance or simply human understanding.
With regard to the Second Amendment, all of these things have changed. It is time for this antiquated piece of law to come down.