When Moral Rules Become Immoral: A Phase-Transition Model of Normative Rigidification

Why do locally correct moral rules generate large-scale systemic dysfunction? This paper argues that the transition from functional moral norms to systemic dysfunction is not gradual but threshold-governed, exhibiting phase-transition-like behaviour at two critical points that separate a functional regime from two structurally distinct modes of collapse. Drawing on a formally validated model of normative dynamics (Motohasi 2025), we interpret the governing parameter as the ratio of normative propagation to contextual updating and show that its variation produces three qualitative regimes. Within the zone of functional normative pluralism, bounded by the two thresholds, a community maintains the evaluative diversity required for contextually responsive moral reasoning while retaining the coherence required for coordinated moral action. Below the lower threshold, propagation dominates and evaluative diversity collapses into moral homogenization: a single normative schema displaces all alternatives, eliminating the community's capacity to perceive and respond to contextually specific harms. Above the upper threshold, normative patterns circulate faster than agents can achieve stable engagement with any framework, producing moral fragmentation: high evaluative diversity coexists with the structural impossibility of coordinated moral response. We characterize the central pathology driving systems toward these collapse regimes as petty moralism---the progressive rigidification of locally correct moral rules into ends in themselves, decoupled from the contextual responsiveness that originally justified them. Case evidence across personal, organizational, historical, and ecological scales confirms the structural signatures of each collapse mode and the asymmetry of the interventions each requires. We conclude by examining implications for moral particularism, structural accounts of injustice, and virtue ethics.