Recap: Moral Foundations Theory (MFT) posits five innate moral intuitions: Care/Harm, Loyalty/Ingroup, Sanctity/Purity, Authority/Respect, and Fairness/Reciprocity. People vary in terms of how much each intuition matters to them. Conservatives tend to be stronger than liberals on Loyalty, Sanctity, and Authority. Liberals tend to be stronger in the Care department. Of course, it’s way more complicated than that, but those are the relevant basics.

MFT continues to evolve. The theory was never intended to be limited to five moral intuitions and researchers have continued to consider additional intuition candidates. Liberty is gaining acceptance as a sixth moral intuition. Conceived both as a freedom from (interference) and a freedom to (pursue happiness), Liberty is especially meaningful to libertarians.  (Duh.)

With Liberty onboard, let’s compare the psychological profiles of the three political sensibilities – conservative, liberal, and libertarian. The following chart is from Iyer et al (2012):

Scale ranges: Moral Foundations Questionnaire: 0-5;  Schwartz Values Scale: 0-8; Ethics Position Questionnaire: 1-5; Adapted to Good Self Scale: 1-4: Liberty Foundation: 0-5

The scale ranges were provided to give a better sense of how much the averages for each group differ. It's one thing to say "Libertarians care less about Harm than Liberals or Conservatives"; it's another to see that we're talking about an average difference of less than 1 point on a 6-point scale. Still significant and interesting but drives home that these differences are matters of degree.

Another point: although the libertarians in this research were self-described libertarians, Iyer et al found a "parallel analyses using social liberalism combined with fiscal conservatism as a proxy for libertarianism in this sample replicated the main findings of this paper." In other words, the approximately 20% of Republicans who are fiscally conservative and socially liberal are a lot like libertarians. So the libertarian profile applies to quite a few Americans. 

Next: looking deeper into the numbers. Plus more numbers.

References:

Haidt, Jonathan (2012). The Righteous Mind: Why Good People are Divided By Politics and Religion. New York: Pantheon Books. pp. 9–11. ISBN 978-0-307-37790-6.

Iyer R, Koleva S, Graham J, Ditto P, Haidt J (2012) Understanding Libertarian Morality: The Psychological Dispositions of Self-Identified Libertarians. PLoS ONE 7(8): e42366. https://doi.org/10.1371/journal.pone.0042366