The Supreme Court's 2008 District of Columbia vs Heller case resulted in a 5-4 split decision. Justice Scalia, writing the majority opinion, held that the Second Amendment was intended to protect the right of individuals to keep and bear arms. Justice Stevens penned a historically related dissent supported by Justices Breyer, Ginsburg, and Souter arguing it protected something entirely different, the militia institutions of the states. Justice Breyer, commenting on the Heller dissent in December of 2010, stated that "historically, the dissenters were right. And I think more of the historians were with us."  This last September, Justice Ginsburg, referencing the dissent indicated that her "view of the Second Amendment is one based on history."  The problem for the dissenting Heller justices is that the historical sources they quote not only fail to support their arguments, but instead directly contradict and prove them to be completely wrong.
The subject under discussion by the Virginia Convention delegates on June 14 was the Constitution's Article 1, Section 8 powers - in this specific case, the militia powers. In order to link its understanding of the Second Amendment to that of Mason, the Heller dissent presents this selection from his speech warning that the states could be deprived of power to arm the militia under the new U.S. Constitution:
[Heller Dissent, p.20]
Following this quote, the dissent discusses the two-clause Second Amendment predecessors from the last three state ratifying conventions of 1788 as if they relate to the militia powers subject Mason was discussing:
"But a number of States did propose to the first Federal Congress amendments reflecting a desire to ensure that the institution of the militia would remain protected under the new Government. The proposed amendments sent by the States of Virginia, North Carolina,and New York focused on the importance of preserving the state militias and reiterated the dangers posed by standing armies."
[Heller Dissent, p.20]
The next quote appearing in the dissent is Virginia's proposed Bill of Rights Second Amendment predecessor, described thus in the dissent:
"The relevant proposals sent by the Virginia Ratifying Convention read as follows: “17th, That the people have a right to keep and bear arms; that a well regulated Militia composed of the body of the people trained to arms is the proper, natural and safe defence of a free State.""
Members of Congress developed the Second Amendment's clauses directly from this 1788 predecessor language. The dissenting justices clearly believe their Mason quote directly related to it. However, the dissenters' Mason quote actually contradicts their views. Why? Because the dissent ignores the fact that Mason did not propose the Second Amendment predecessor in his June 14th speech. In fact, he never mentioned any Second Amendment related predecessor or language in relation to the militia powers subject under discussion that day. He did, however, propose an entirely different amendment directly addressing the subject of his speech that the dissent simply ignored.
This is the militia powers amendment Mason proposed on June 14:
"I wish that, in case the general government should neglect to arm and discipline the militia, there should be an express declaration that the state governments might arm and discipline them. With this single exception, I would agree to this part"
The dissenting justices not only overlooked Mason's actual proposal from June 14, above, they also completely ignored Article 11 in Mason's list of "other" amendments adopted by the Virginia Ratifying Convention that directly related to his militia powers proposal and speech:
"11th. That each state respectively shall have the power to provide for organizing, arming, and disciplining its own militia, whensoever Congress shall omit or neglect to provide for the same."
George Mason's June 14, 1788 speech not only fails to support the dissent view of Second Amendment's intent, it proves the Heller dissent to be completely wrong about its intent. Mason's state militia power proposal of that date directly related to Article 11 of the "other" amendments proposed by Virginia, not to the Second Amendment predecessor. Since Mason prepared all of Virginia's amendments, and because he indicated the Article 11 related protection was the only change needed to the militia arming powers, it is clear the Second Amendment proposal from Virginia was not understood by him as protecting state militia authority. In an erroneous attempt to demonstrate Mason's view matched those of the dissenting Heller justices, the dissent simply appropriated the clear intent of Virginia's Article 11 militia powers amendment and reassigned it to the entirely separate and distinct Second Amendment predecessor found in Virginia's list of Bill of Rights protections. Mason's speech makes no such connection and, in fact, contradicts any such link.
Mason's quote in the Heller dissent is its sole piece of period evidence indicating the Founders and dissent share the same view of Second Amendment intent. The dissenting justices' misinterpretation of their Mason speech snippet conclusively demonstrates that the dissent view of Second Amendment intent is founded on an erroneous conflation of intent with an entirely different amendment. Mason's complete comments on June 14, 1788, demonstrate the Heller dissent historical arguments to be based on a foundation of factual error.