How can we explain the court's anti-gun control ruling in Parker v. District of Columbia?

I happen to agree with Fz's reading of the Second Amendment: namely, that it protects the right to bear arms purely for the purpose of establishing a well-regulated militia. So why didn't the Court of Appeals for DC follow this line of reasoning in Parker v. District of Columbia? Well, an article that ran in the New York Times a while back argued that liberal legal scholars, of all people, were the main force behind a general change in the interpretation of the Second Amendment:

There used to be an almost complete scholarly and judicial consensus that the Second Amendment protects only a collective right of the states to maintain militias. That consensus no longer exists — thanks largely to the work over the last 20 years of several leading liberal law professors, who have come to embrace the view that the Second Amendment protects an individual right to own guns.

In those two decades, breakneck speed by the standards of constitutional law, they have helped to reshape the debate over gun rights in the United States. Their work culminated in the March decision, Parker v. District of Columbia, and it will doubtless play a major role should the case reach the United States Supreme Court.

Laurence H. Tribe, a law professor at Harvard, said he had come to believe that the Second Amendment protected an individual right.

“My conclusion came as something of a surprise to me, and an unwelcome surprise,” Professor Tribe said. “I have always supported as a matter of policy very comprehensive gun control.”

Clearly, the liberal legal scholars didn't intend for this to happen; but they were forced to embrace an individual-rights interpretation of the Second Amendment by their own philosophy of expansively interpreting the Constitution. Not everyone, however, is willing to give so much credit (or blame) to the liberals for this sea change in constitutional interpretation. Jack Balkin credits larger forces:

If the Supreme Court eventually holds that the Second Amendment protects an individual right, it will largely be because social and political movements changed popular opinion and influenced elite legal opinion. These changes have been coming for some time: The Bush Justice Department has already adopted the individual rights position, and so too has the D.C. Circuit in its recent Parker opinion.

And Randy Barnett at the Volokh Conspiracy thinks we're ignoring the obvious:

What the story leaves out, of course, are the prodigious efforts of those "libertarian" and "conservative" constitutional scholars who did much of the heavy lifting when it comes to the original meaning of the Second Amendment AND the original meaning of the Privileges or Immunities Clause of the Fourteenth Amendment.