Actively Open-Minded Thinking (AOT) is a set of standards for rational thinking. Because the thinking of citizens and officials affects political decisions, good thinking is a moral virtue, like honesty. AOT standards have two functions: people try to follow their own standards; and they apply these standards to the evaluation of the thinking of others. The second function is especially important in public policy, where most of us often ``outsource'' our thinking to others. Individual differences in AOT primarily involve two dimensions: open-mindedness, avoiding ``myside bias''; and overconfidence in a favored conclusion. The most dangerous political beliefs are those that are held with great confidence despite minimal or biased thinking. Here we review the recent literature on the role of AOT (as a standard, and the correlations between AOT measures and particular political beliefs, such as acceptance of conspiracy theories. We argue for a ``positive manifold'' in which Enlightenment-based ideas about thinking and politics are all correlated with each other. We then report a study that tries to find the source of individual differences in this sort of ``cognitive liberalism'' and associated beliefs, comparing two major accounts: cultural background and thinking by oneself. We find evidence for both influences. But people often regard themselves as rebelling against their background, despite its actual influence on them.