Have you actually tested them for rationalizing? My own beliefs are that it's more likely to run into someone who rationalizes so much they are blind to their own rationalizing (and so can't recall any) than someone who is inhumanly honest.
(Tests in this case would include checking for hindsight bias, which is classic rationalizing, and having them do that test on YourMorals whose name I forget where you're given two summaries of studies for and against gun control and asked to criticize them - usually showing imbalance towards your favored side. But you're a LWer, I'm sure you can think of other tests.)
Anna Salamon and I are confused. Both of us notice ourselves rationalizing on pretty much a daily basis and have to apply techniques like the Litany of Tarski pretty regularly. But in several of our test sessions for teaching rationality, a handful of people report never rationalizing and seem to have little clue what Tarski is for. They don't relate to any examples we give, whether fictitious or actual personal examples from our lives. Some of these people show signs of being rather high-level rationalists overall, although some don't.