<p>In 2015, Behavioral and Brain Sciences published a symposium on the implications of left-leaning ideological imbalance in social science, with a lead article from Duarte et al. calling for the fostering of greater political diversity. In this essay I revisit, reaffirm, and extend this call. First, I review two prominent theories of viewpoint diversity from Mill and Longino, demonstrating the irreducible need for actual viewpoint diversity in knowledge production and the inadequacy of proposed alternatives. Second, I distinguish between two types of ideological imbalance (scholar-activism vs. paradigmatic progressivism) and two types of political diversity (ecumenical heterodoxy vs. perspectival pluralism), examining the implications of each for the effective epistemic functioning of social science. Based on this assessment, I argue that the fostering of distinct alternative paradigms is needed to address threats to validity stemming from ideological imbalance. Third, I offer a targeted claim:&#xa0;The development of a conservative paradigm is a minimal necessary measure to meet the conditions of adequate viewpoint diversity as formulated by Mill and Longino. Conservative perspectives should be actively fostered. Anticipating concerns about ideological science, I clarify how a conservative paradigm can uphold core scientific norms while offering essential critique and opening new avenues of inquiry.</p>