I've been listening to the archives of Ideas and Issues, a show that Hugh LaFollette of East Tennessee State University hosted until it lost funding in mid-2003. In the 2002-03 season of the show he followed up every interview with an author with two critiques from other experts. His conversations with George Fletcher, Bruce Ackerman and Eric Segall about Fletcher's book Our Secret Constitution: How Lincoln Redefined American Democracy are particularly interesting. The thesis of the book is that the reconstruction amendements were so radical that they practically created a new constitution. I enjoyed Segall since he touches on the issue of judicial activism. As a liberal in favor of liberties over freedoms, he believes that the SC should be more deferential to Congress, and thus more prone to support liberties. He mentions that the conservative criticisms of the Warren court's activism were an anomaly because most critics of judicial activism come from the left. Not being an expert on the topic, I can't comment on how accurate he is.
It would be helpful to sort sort controversial judicial decisions into three types: overturning state laws, overturning federal laws, and "legislating from the bench." I think the first two types can be fairly labeled activism, whereas the third type is only labeled activism by opponents of the verdict post hoc.