If the terms "judicial activism" and "judicial restraint" have any meaning, it is that a court is activist when it is invalidating laws and overruling precedent, and restrained when deferring to popularly elected legislatures and following prior decisions.
Never before had the Supreme Court found that the 2nd Amendment bestows on individuals a right to have guns. In fact, in 1939 (and other occasions), the court rejected this view. In effectively overturning these prior decisions, the court both ignored precedent and invalidated a law adopted by a popularly elected government.
What's more, the court's interpretation is questionable. The text of the 2nd Amendment is ambiguous. Its second clause speaks of a right to "keep and bear arms," but its first clause suggests that this right exists because a "well-regulated militia" is essential. There is thus strong reason to believe that the 2nd Amendment only guarantees gun rights for those serving in a militia.
At the very least, one would expect that a high court committed to judicial restraint would have used the 2nd Amendment's ambiguity to defer to the political process and to follow precedent. Yet nowhere in Scalia's opinion was there mention of the need for judicial deference that is so characteristic of his opinions in cases involving other individual liberties.
What then explains the court's decision to strike down the D.C. law? Conservative political ideology. The majority followed prevailing conservative political philosophy and found that the 2nd Amendment bestows on individuals a right to have guns.
This should not be surprising. The conservative justices regularly jettison judicial restraint when it is at odds with conservative politics. They've done the same thing in cases involving affirmative action and desegregation programs.
The irony is that the same conservative justices who were so eager Thursday to find an individual liberty under the 2nd Amendment are loath to do so when a right of a criminal defendant is at stake or when it is a matter of enforcing the religion clauses of the 1st Amendment. Thursday's decision is a powerful reminder that the conservative justices are activists when it serves their political agenda.
Erwin Chemerinsky is the dean of the UC Irvine School of Law.