Stare decisis. Most people have no idea what that phrase means. People who do tend to care a lot about it. It's the rule of precedent in law; the common-law notion that that which has been decided before should determine--or at least influence--decisions that follow.
Nowadays, when people talk about stare decisis, unless they are at a legal convention, they almost always mean 'abortion' and Roe v. Wade. "Will you uphold stare decisis?" asks a senator. "Yes," responds the potential justice. Translated: "Will you vote to uphold Roe v. Wade?" "Maybe."
Politico has an article about certain Senate Democrats being p.o.'ed about Justice Roberts and Alito, saying that they 'misrepresented themselves' in their confirmation hearings. First off, that's BS. They were very honest. Cagey, but honest. Roberts said that Roe would have the practice of stare decisis applied to it. Alito said something similar. What neither mentioned--though both undoubtedly believe--is that according to the principle, decisions made that were incorrect (e.g. Plessy v. Ferguson) should be overturned (e.g. Brown v. Board of Education).
Frankly, every decision rendered by the Supreme Court either ignores or alters some precedent. If you ever read opposing briefs from opposing sides in a case, you'll find that both use old Supreme Court cases to support their own arguments. The justices then determine which precedents do (or should) apply and which don't. Sometimes, precedents are obvious (abortion: Roe v. Wade, Planned Parenthood v. Casey, Gonzales v. Carhart; segregation: Plessy v. Ferguson, Brown v. Board of Education), so when they are ignored or altered, it is quite noticeable. Sometimes, they are somewhat ambiguous.
So, basically, what I'm saying is that stare decisis doesn't mean everything stays the same, and arguing that justices 'misrepresented themselves' by saying they would 'follow precedent' is as dumb as calling someone a 'strict constructionist'. Alito and Roberts are simply doing what they were appointed to do: determining which precedent is in line with the Constitution and which is not. The fact that Dick Durbin doesn't like it doesn't make them liars.
P.S. It is really, really dumb to define 'judicial activism' as 'when a court overturns a past ruling.' Criticisms of judicial activism have never been about overturning precedent. They have always been about the Supreme Court taking upon itself prerogatives that are granted to the executive and the legislative branches ("legislating from the bench"). It's a fuzzy line, admittedly. The Court always sets standards on how a law should be interpreted. Those standards could be, broadly, considered 'legislating', since Congress didn't tell them what to do. The more obvious cases, however, are items like Griswold v. Connecticut, where the Supremes decided that the State cannot legally keep people from using birth control, since there is a right to privacy. The fact that a right to privacy (beyond illegal searches and seizures) is not directly mentioned in the Constitution angers some people, making them feel the Court has overstepped its bounds. That leads to a vague term--'activism'--which, if anything, is certainly not to be construed as 'overturning precedent.' Let's all just deal with the fact that the term is not quantifiable and is different depending on who's talking.