"Today, being pro- or anti-vaccine has become essential to many people’s social identity during the pandemic. William Bernstein, a neurologist and author of The Delusions of Crowds, pointed me to the “moral foundations” theory, which attempts to understand what motivates the decision-making of people on the right and left ends of the political spectrum. That theory holds that, within the American right, the concepts of loyalty and betrayal are more influential to their worldview than on the American left. Staying true to your group is a powerful pull for conservatives. “For these folks, facts mean nothing; membership and identity, everything,” Bernstein said over email. “Groupishness, in-/out-group differentiation ... is much stronger on the right.”"