The left's latest move in judicial politics is to redefine the concept of judicial restraint. This is necessary because no one thinks that judicial activism is a good thing. The reason has nothing to do with talk radio and conservative demagoguery. It's rooted in the implications of judicial review. If we give judges the power to frustrate the decisions of elected officials, then they need to base that power in something other than their own policy preferences; something that has itself been legitimized by popular assent.
Jeffrey Rosen is probably the principal popularizer of a supposedly "neutral" definition of judicial restraint that reduces it to a question of striking down statutes (or, I suppose, invalidating executive actions.) There are three problems with this approach.
First, it is rooted in an assumption that there can be no substantive definition of restraint that is rooted in an understanding of constitutional or statutory text because the texts are too elastic to bear any definite meaning. This is a point of view that has the most attraction for certain law professors and law students who, I think, are overly impressed with their verbal dexterity. More fundamentally, it is a premise that restraintists don't share. Interpreting law is not a mechanical process and reasonable people can differ, but texts are not just convenient starting points.
Second, it elides the debate over restraint and activism (which is really a debate between competing schools of interpretive theory) into a debate over judicial review itself. That's a worthy debate, but restraintists don't oppose judicial review.
Third, it runs contrary to a central precept of judicial restraint, i.e., that judges may not ignore clear constitutional commands. If a legislative or executive action falls runs afoul of such a command, the refusal to strike it down is "activist" in the sense of exercising authority from some illegitimate source.
Another part of this move is to conflate judicial restraint with stare decisis. These concepts may be related but they are not the same and restraint does not mean adhering to erroneous precedent.
Thus, Arlen Spector is upset that the Roberts court has abandoned or weakened precedent and wants to investigate the Roberts and Alito confirmation hearings. But Roberts and Alito never said that they would always follow precedent or that it must always be expanded and never narrowed.