Activist judges

This Op-Ed from the NYTimes makes a great point about who the real "activists" are on the Supreme Court today.
The authors use a formula by which they determine how much of an activist each current justice is based on the percentage of times they have voted to overturn Congressional legislation.

Declaring an act of Congress unconstitutional is the boldest thing a judge can do. That's because Congress, as an elected legislative body representing the entire nation, makes decisions that can be presumed to possess a high degree of democratic legitimacy. In an 1867 decision, the Supreme Court itself described striking down Congressional legislation as an act "of great delicacy, and only to be performed where the repugnancy is clear." Until 1991, the court struck down an average of about one Congressional statute every two years. Between 1791 and 1858, only two such invalidations occurred.

Since the Supreme Court assumed its current composition in 1994, by our count it has upheld or struck down 64 Congressional provisions. That legislation has concerned Social Security, church and state, and campaign finance, among many other issues. We examined the court's decisions in these cases and looked at how each justice voted, regardless of whether he or she concurred with the majority or dissented.

Here is how the justices came out:

Thomas 65.63 %
Kennedy 64.06 %
Scalia 56.25 %
Rehnquist 46.88 %
O’Connor 46.77 %
Souter 42.19 %
Stevens 39.34 %
Ginsburg 39.06 %
Breyer 28.13 %

It is pretty clear that by this measure the "conservative" justices are more likely to intervene and strike down legislation than the "liberal" justices.
So who are the real "activists" in this case?